“It is more efficient to turn gas into electricity”
I don’t think that’s correct. It may be true for highly variable/low loads where the pumping losses in the pistons dominates. However the majority of fuel consumption in a car happens at traveling speed (highway miles). That is the area that needs to be optimized for.
My 2015 Honda Accord Hybrid takes this approach. At below-freeway speeds the gas motor runs in series to drive an electric motor. At highway speeds, it engages a clutch and directly connects the engine to a low-loss 1-speed transmission.
> However the majority of fuel consumption in a car happens at traveling speed (highway miles).
Unless of course you drive primarily in stop-and-go traffic, e.g. delivery drivers, taxis, commuter cars, etc. Quite often you won't exceed 50 kph. For whatever reason, I've never seen (or have and forgotten) a car marketed towards this market—probably for exactly the reason that plug-in hybrids perform better in this scenario.
> > “It is more efficient to turn gas into electricity”
> I don’t think that’s correct.
You're right, it's not.
In fact, GM wrote an SAE paper about their "2-mode hybrid" transmission (which was used in their 2008-2013 light-duty trucks and SUVs, and then in later modified form in the 2nd gen Volt), where this is plainly explained.
In the paper they describe exactly the tradeoffs made to optimize fuel efficiency in an eCVT... it turns out that you want to set up the planetary gears to minimize the energy transmitted from input to output via electricity and maximize the amount transmitted mechanically because that is most efficient. You especially want to avoid a round trip through the battery in most cases (except when that allows installing a smaller, more efficient ICE).
That has implications for the CVT's mechanical ratio: GM's "2 mode" which has what basically amounts to an auxiliary overdrive integrated in the eCVT so that it can use smaller motor-generators over a wider range of speeds. Smaller motor-generators means more energy is transmitted mechanically, which means higher efficiency.
This is also basically the same reason the 1st gen Volt gets significantly worse highway MPG in range-extender mode than the (contemporary) Prius Hybrid (~35MPG vs ~50MPG): The 1st gen Volt eCVT was envisioned as an EV with a range extender (where energy usually comes from a battery), while the Prius's eCVT was optimized for driving primarily on the ICE, with the battery only supplementing acceleration.
I don’t think that’s correct. It may be true for highly variable/low loads where the pumping losses in the pistons dominates. However the majority of fuel consumption in a car happens at traveling speed (highway miles). That is the area that needs to be optimized for.
My 2015 Honda Accord Hybrid takes this approach. At below-freeway speeds the gas motor runs in series to drive an electric motor. At highway speeds, it engages a clutch and directly connects the engine to a low-loss 1-speed transmission.