@miscacc Clicked around a bit and found the English page, the word we're looking for is Diesel multiple unit:
https://en.wikipedia.org/wiki/Diesel_multiple_unit
There are a bunch of them from all around the world. In the Hungarian example, the whole engine is basically under the floor.
@miscacc @Shento
If the engine is small enough, it doesn't need a dedicated compartment. It's not from Japan, but from Hungary, but have a look at this, it can move on its own:
https://hu.wikipedia.org/wiki/Bzmot#/media/File:Bzmot-268_sp.jpg