It can be an involved topic but to try and summarize it as best I can. Cooled EGR can remove heat from the combustion chamber moreso than just using the VVT to create an internal EGR effect. The exhaust cam has a little different opening and closing events and is used in conjunction with the EGR.
The cooling effect of the EGR is used to help control knock by putting an inert gas into the combustion chamber while still keeping good spark advance and not having to inject more fuel during higher load scenarios. That contributes to a slight fuel economy bump and lower NOX emissions. The tumble flaps added to the intake manifold help contribute to even mixing of the air charge when EGR is active. More and more OEMs are playing with cooled EGR systems. The Skyactiv-Z will have a significant bump in EGR use in comparison to what we see now.
