Featured Audi mild-hybrid systems

Looks like Audi's jumping on the mild hybrid boat: Green Car Congress: Audi’s mild-hybrid systems: 12V for 4-cylinders, 48V for 6- and 8-cylinders

So, basically, there's a few interesting things going on here.

First off is that they're apparently moving almost everything to a 48 volt bus on larger vehicles, not just the hybrid system. This is almost certainly an attempt to reduce wiring weight throughout the vehicle (on vehicles that are relatively cost-insensitive) - the electronics already need DC-DC converters to go down from 12, so...

Second is that the 4-cylinder systems are apparently running mild hybrids on 12 volts, likely for cost reasons. That will limit power, and when they're talking about 12 kW on the 48 volt system... it won't do much.

Third is that they're implementing engine-off sailing. For a few years now, VAG's automatic transmissions have had an available (but often deactivated) coasting mode which automatically disengages the engine from the wheels whenever the driver lifts off the accelerator, but it leaves it running. However, on the original 1-Liter-Auto concept in 2002 (which was also a mild hybrid), they also shut the engine down when doing this... and they're implementing that on these mild hybrids. That could improve efficiency significantly, although the engine will have to be started and engaged to the wheels to perform regenerative braking