I asked this of a friend of mine (an American) who works in Germany for a German automotive powertrain supplier. His response:
"Well, I don't know that I have ever seen it explicitly stated as such on a
business card or anything, but there are many different terms. Do you mean
engine, transmission, the rest of the driveline, or the whole shebang? In
English we usually lump it all together under that generic 'powertrain'
term. There is a term (actually, several different ones) for everything
from (not including) the engine up to the wheels, but I think you're
looking for something including the engine, right?"
His follow-up:
"If you are talking about everything from the engine to the wheels, I'd use
Kraftübertragungs, Antriebsgruppe, or Kraftübertragungssystem Ingeneiur.
Engine specific- Motor or Triebwerk."
Hope this helps.
Brad