[dcb]

There is plenty lapses in logic to go around Mech, i.e. "500 hp in your hand" (but ZERO mention of efficiency at that rating, which is the entire point of this forum, and which is historically atrocious for hydraulic systems at higher RPMs), or saying a hydraulic doesn't have a driveline (it damn well does, only it has to pump gobs of fluid under very high pressure through fairly small pipes).

But it still remains that ANY energy transformation from an ICE to the wheels will have losses, and if you are operating at relatively constant speed and load then you can tune a direct drive ICE to higher peak overall vehicle efficiency than either electric or hydraulic drivelines.

Being primarily a flatlander, and fancying myself an efficiency aware driver, and something of a cheapskate, I should see the least fuel usage AND the leasts costs with a simple "hiway use" ICE for parallel setup, period. To me these series hybrid range extenders are inherently less efficient in this range extending role.

And back to the OP, that is the problem, series is crippled by inherent conversion losses that reduce its peak efficiency, so can we talk about what those losses are so we can quantify the problem? Lets say we have a vehicle moving at a certain speed on a flat road:

if you assume an electric motor is 90% efficient, and a generator is 90%, and a controller is 95%, the "transmission" here is %77 efficient, and is noticably more complicated and costly than a chain and sprocket driving a wheel.

The hydraulics I've seen are for big and slow, moving launching pads around and stuff. Trying to move a relatively thick fluid through pipes quickly will incur dramatic pressure drops and efficiency drops, so the dynamic range of hydraulics (while retaining near peak efficiency) is not good at all without very large pipes and hoses and motors. And for fixed speed/load driving like I am describing in the original post, I'll take direct drive for even more peak efficiency and less cost and weight and complexity and maintenance and ???.