In the mbusa.com Vehicle Features section for various mild hybrid vehicles like the GLE450, CLS53, etc. there is confusing information and photos regarding the hybrid configuration.

QUESTIONS: Is the small "starter/generator" pictured at the front of the engine as part of the mild hybrid configuration redundant with the "flywheel/motor/generator/starter" used in the M256 engine on the E53 and CLS53? Does the engine in the GLE580 include the flywheel unit or only the small unit? Is the small unit belt driven?

For some vehicles such as the GLE450, the photos show both a separate small "starter/generator" at the front of the engine AND a flywheel unit that in the past has been called an "integrated flywheel/motor/starter/generator". For other vehicles like the GLE53, only the small unit is shown with no photo of the flywheel unit. For the CLS53 only the front of the engine is shown with what appears to be the small unit at the front with no reference to the flywheel unit. The E450 engine photo clearly shows a belt-driven unit with no reference to the flywheel unit. The E53 clearly shows the flywheel unit and refers to it as the "Integrated Starter Generator" with no reference to a separate small belt-driven unit.

It seems to me that a belt-driven starter is a potential weak link. And I question whether a small unit at the front of the engine can supply significant torque to the drivetrain. So in all of these engines, is there a flywheel motor that boosts HP and torque like on my CLS53? Am I going to get a belt-driven starter on the GLE580 that I have on order? Is the configuration changing to include only the belt-driven unit? Can someone please clarify how these mild hybrids are configured? Thanks for your info.

Here are the relevant photos taken from mbusa.com: The flywheel unit and the small starter/generator:

 

Without any help for MB but through discussion on another forum, we have decided that the separate unit pictured above is the 48-volt drive air conditioner pump, in spite of the photo being labeled "EQ Boost Integrated Starter-Generator." Very poor marketing of the mild-hybrid system with focus on "Starter-Generator" rather than the "Motor" feature of the flywheel unit. Every car has a starter and a generator/alternator but what is special is the motor/flywheel feature that adds 21hp and a huge amount of torque.