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Comment by ghostly_s | Hacker News Reader

> The Wankel is at its most efficient and its most reliable when operating at a constant RPM. Conveniently, the EV generator application demands a pretty flat RPM band.

If I understand the article correctly, the "series" hybrid configuration means precisely that it cannot operate at the ideal rpm when charging the battery, because it is always driving the wheels directly as well.

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Exactly the opposite. In a series hybrid, there is no mechanical connection between the engine and the wheels - only an electrical one, with the battery still providing considerable power in most cases, even when it's depleted.

No hybrid ever runs its battery all the way to zero, and series hybrids are no exception. The Chevy Volt (the other notable series hybrid in Western markets) keeps its engine at a near-constant RPM by using the battery to supply torque, even when the battery is "dead." I would expect the MX-30 to do the same.

IME in several thousand miles driving/riding in a Volt, it hums away within a very narrow RPM band unless you hoon it on a dead battery in cold weather. Even then, it's not nearly as wide of a rev band as a conventional hybrid.

The Volt is a series/parallel hybrid. It has situations where the motor is directly connected to the wheels. The BMW i3 does has a series only set up, but that’s probably because it also has a BEV only version.

The part that's got me confused is the illustration near the end, with the caption: "In the MX-30 e-Skyactiv R-EV’s electric propulsion unit, the already compact rotary engine shares a common axle with the generator and motor."

I don't get how the engine can be decoupled from the wheels if it's mounted to the same axle as the motor?

I think you have series and parallel hybrids backwards. Series hybrids have no mechanical connection between engine and wheels. It's just an EV with a generator wired in.

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