Doing some research on how the FEH drivetrain really works (thanks goes to respondents in other threads) I learned even the gas engine is different from a conventional four banger. Its an Atkinson engine, which uses an uncommon design first developed in the late 1800s. It eliminates the camshaft normally found in many conventional engines, which is used to open and close valves during the 4 stroke process. A conventional engine actually needs a couple of turns of the crankshaft, which turns a camshaft connected by timing gears or belts, in order to accomplish this. The Atkinson design manages this in one turn of the crankshaft with NO camshaft and no timing belts, chains or gears.

There is an animated web site that shows how the original Atkinson design worked:

http://www.keveney.com/Atkinson.html

 

But, as some have noted, the FEH Atkinson is not exactly like the animation; the same effect is achieved through different means (changes in the valve timing, I think). See the thread entitled "Animations of Engine Types" in the "Fuel & Emissions" forum.

 

The ICE in the FEH (and Prius) is Atkinson-like. It does vary the stroke length, but not by mechanical means. I believe there is still a cam shaft, but the valve timing is controlled to get the Atkinson effect and benefits.

The original Atkinson design was never successful due to its mechanical complexity.

JeffD

 

I believe the original atkinson does have cams but they are located on the main crankshaft. I'm not sure how it's done on the new hybrid ICE's. And I wonder if the crank only turns one rev for each complete cycle??? Someone here must know for sure.

 

No it does not. The Prius and FEH engines only mimick the Atkinson cycle in volumetric expansion vs. compression through valve timing. Think of a regular engine with REALLY bad valve timing. That is basically what it is.