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@TechConnectify so, on the serial implementations.
purely serial hybrids have another Achilles heel than just conversion losses: the size (and weight, and cost) of the MGUs. note that the Toyota MG1 and MG2 are pretty small - the fact that a significant percentage of ICE torque goes through a mechanical path, bypassing the serial path, means that MG2 needs to only be sized to take battery+MG1 power, not battery+full ICE power as a serial hybrid would need.
Nissan’s e-Power system, which is purely a serial hybrid, isn’t terribly inefficient at low speeds as I understand - a bit worse than the Toyota system in comparable models, but not much - but falls completely on its face at non-Japanese (that is to say, faster than 100 km/h) highway speeds. the real reason why Nissan made it was they had Gen 1 LEAF motors lying around, and they could reuse them in a serial hybrid system.
your Gen 1 Volt wasn’t purely a serial hybrid, and it had a few different modes it could operate in, one of which was a single-speed parallel hybrid mode, specifically to avoid the conversion losses of serial hybrid operation when on the highway. (the other notable improvement over a pure serial hybrid was that it could disconnect MGA from the ICE and connect it to the wheels, when high electric power was requested, so that MGB could be somewhat smaller/lighter/cheaper.) as I understand, the big efficiency problem the Gen 1 Volt had wasn’t really the hybrid system, it was that the engine tuning was not complete and they didn’t get a chance to optimize efficiency, only to get it to comply with emissions (and that they run super high EGTs to keep the catalytic converter hot, and then just keep running at those super high EGTs all the time).
that said, a better comparison may be to Honda i-MMD - similar engine efficiency to Toyota’s best, and a similar serial-hybrid with a single-speed parallel hybrid mode. this does… pretty well, despite not having the Gen 1 Volt optimization of an undersized traction motor and repurposing the generator as a second traction motor in EV mode.
…and then there’s the Chinese automakers. as far as I can tell, most of the Chinese systems are essentially developments of the Honda i-MMD or Mitsubishi Outlander PHEV (same idea as i-MMD) concept, with the addition of a 2-4-speed gearbox (possibly a DCT) to allow the ICE to connect to the axle at multiple gear ratios. BYD’s system is, I believe, “what if we just did the Gen 1 Volt system but better?” these seem to be doing shockingly well, but I’m sure some of this is BYD and Geely breaking 46% peak thermal efficiency, when the best Toyota can do is 41%.
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@TechConnectify on patents: for GM specifically, I don’t think this was an issue at all. GM was making two-mode power-split transmissions as early as 2003 (the Allison EP40/EP50, now known as the H40EP and H50EP), and selling consumer vehicles with them in 2008 (the 2ML70 used in the GMT hybrids, as well as the BMW, Chrysler, and Mercedes vehicles using that powertrain). and, the Gen 2 Volt basically used a scaled down version of the Allison EP system.
for other automakers, maybe? but, yeah the patents are dead now.
and, finally, for locomotives… as I understand the problem there isn’t torque output per se - gearing turns horsepower into torque - but rather making the kind of gearbox that has wide enough range to get a 2 mile long consist moving from a stop uphill, as well as to go 80 MPH, while surviving behind a 3-4000 hp diesel. diesel-hydraulic systems using torque converter automatics are a thing in DMUs that have multiple smaller engines, but not so much in locomotives. (also, with longitudinal engines, you’d have to turn the power 90 degrees and eat some losses there. and, with a diesel-electric, you get dynamic braking for free as an additional way to slow the locomotive down.)
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@bhtooefr @TechConnectify
Nissan's e-Power drives exactly like a BEV, which makes it very comfortable and gives you stronger brake regeneration.
It is less efficient at high speeds than Toyota's system, but I personally prefer driving e-Power, it feels smoother. It's essentially a BEV with an onboard generator, after all. The video puts heavy emphasis on the efficiency shortcomings, but in reality e-Power has nothing to be ashamed of. I find that part quite misleading.
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