One thing that always puzzled me was how the gas engines in hybrids were so efficient. Technology Connections has a great video explainer: <a href="https://www.youtube.com/watch?v=KnUFH5GX_fI" rel="nofollow">https://www.youtube.com/watch?v=KnUFH5GX_fI
tl;dw: constant RPM and a weird stroke geometry where the power stroke is longer than the other strokes to extract more energy from the expanding gasses.
I'm surprised there isn't more effort to create hybrids in reverse--an electric car with optional gas generator. The gas generator could run at constant speed, never changing RMP, while the battery handles constant changes in acceleration. The idea is not mine. I've heard about it in China
There were several of them: the first and second generations of Chevy Volt, Fisker Karma, BMW i3, and a couple of Chinese brands.
They're less efficient than parallel hybrids at high speeds (on a freeway). And you also need a fairly sizeable engine to keep up with the consumption at freeway speed, so at this point you might as well just throw in a planetary gearbox.
The Chevy Volt (and it's predecessor the GM 2-mode hybrid, and the Allison power-split hybrid) was a work of art. It is fundamentally a planetary gearbox, with 2 motor-generators.
In ICE mode, under 35 MPH, it worked as a series hybrid. Above 35, the engine mechanically connected to the wheels. One motor-gen extracted power and fed it to the other, acting as a CVT in parallel. This provided the ratio changes needed for the small engine.
It was way too complicated and expensive the two times they tried it (2008, then the Volt). It was successful and lives on to this day in its original application: city buses.
Planetary gear plus 2 motor-generators is 'Toyota Synergy Drive' and also used by Ford and Stellantis in some hybrid models. At least the Ford C-Max and Chrysler Pacifica hybrids use this style drive train. I'm not on top of all the hybrids, but I'd guess if 4 car makers do it, there's others to be found.
It makes a lot of sense, works well, and is very durable... as long as Ford didn't forget to heat treat a bearing or whatever they messed up in early C-Maxes.
gcanyon · · focus · HN ↗
tl;dw: constant RPM and a weird stroke geometry where the power stroke is longer than the other strokes to extract more energy from the expanding gasses.
jostmey · · focus · HN ↗
cyberax · · focus · HN ↗
They're less efficient than parallel hybrids at high speeds (on a freeway). And you also need a fairly sizeable engine to keep up with the consumption at freeway speed, so at this point you might as well just throw in a planetary gearbox.
sam1714 · · focus · HN ↗
In ICE mode, under 35 MPH, it worked as a series hybrid. Above 35, the engine mechanically connected to the wheels. One motor-gen extracted power and fed it to the other, acting as a CVT in parallel. This provided the ratio changes needed for the small engine.
It was way too complicated and expensive the two times they tried it (2008, then the Volt). It was successful and lives on to this day in its original application: city buses.
toast0 · · focus · HN ↗
It makes a lot of sense, works well, and is very durable... as long as Ford didn't forget to heat treat a bearing or whatever they messed up in early C-Maxes.