Just stoking the fire with more info:
This Toyota press release about the new hybrid system in the 3rd gen Prius & dedicated Lexus 450h hybrid discusses the 2 aims of their
cooled EGR approach.
1) manage EGR to
reduce exhaust gas temps in high-load situations (hills & freeway driving) to avoid needing to go to fuel enrichment (which also reduces EGT) to protect the catalysts; and
2) reduced pumping losses
Quote:
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The cooled EGR system allows precisely metered and spent exhaust gas to enter the intake system, lowering exhaust gas temperature while also reducing engine pumping losses via decreased intake vacuum. An EGR delivery manifold ensures even distribution of the exhaust gasses to all cylinders. The high-capacity EGR cooling system can reduce the gas temperatures from about 880˚ C to 150˚ C, improving volumetric efficiency. The cooled EGR also eliminated the need for exhaust VVT-i.
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