REEVs and PHEVs: A Distinction, or a Difference?

"However, the Volt and Prius clearly demonstrate that the contrast between an “REEV” and a “PHEV” is a bit more than a semantic difference, despite the similar basic architecture."

Though the marketing "geniuses" at GM decided to use their own term - PHEV is the generic term. You have a "mostly" serial PHEV like Volt (or a real serial PHEV like Karma or BMW i3) - or a serial/parallel PHEV like Prius PHV or Energi. They are all PHEVs.

Here is the response that I got from Toyota:
"Yegor, the 2012 Prius PHV that was unveiled at the Frankfurt autoshow this year does showcase that the production Prius PHV will have a user-selectable "EV mode" allowing the driver to select when to be in EV-only mode. The "EV mode" allows the driver to accelerate normally to 100km/h with electric-only propulsion. The gasoline engine only turns on when extremely high-load demand is required."

Clearly a lot of the folks here speak a different version of English than I do and have little understanding of how the Volt or Prius works:

@theflew

"There's nothing in the "serial hybrid handbook" that says anything about the design of a serial hybrid not having clutches, gears, etc...
True with that "serial hybrid handbook" but Merriam-Webster defines "Serial" as:
of, relating to, consisting of, or arranged in a series, rank, or row

where "series" is defined as:

a number of things or events of the same class coming one after another in spatial or temporal succession.

Nothing in the Volt or Prius drivetrain is a number of things coming one after another in spatial or temporal succession. All 3 motors feed into a single mechanical transmission.

You might be able to argue that the Honda hybrid design is serial since both motors are on the same mechanical shaft. In this case, the Honda would be a "mechanical series" while the Fisker is an "electrical series" design.

@JeffN
I don't think you've sat through GM's explanation and justification of their Rube-Goldberg drivetrain

"Neither the Prius or Volt can strictly operate in parallel mode -- the gas engine by itself would just sit and spin the planetary gears."
Actually, the Volt has a brake that locks down the inputs to the transmission to keep inputs from being driven. It also has clutches to enable engagement and disengagement of various inputs and outputs to the transmission.

You are correct about the Prius (and other Toyota hybrid drivetrains). The ICE would be spun backwards if the electric motor were to push very hard. This is part of why it must start up for strong acceleration. The other part, of course, is that the electric motor/battery is too weak for strong acceleration.

@JeffN,

It sounds like we were probably in the same room together! Was that the Volt CAB event that Chelsea Sexton set up?

Unfortunately, I don't have copies of the powertrain schematic and I don't recall for certain if there are brakes on the electric motors so I'll take your word. Regardless, the electric motor can probably be held electrically if there is no friction brake to hold the Sun gear.

I guess you're saying that if the ICE is driving the small electric motor and the large electric motor is driving the wheels through the planetary transmission, then it is a series topography.

I suppose if you squint a little, that's a valid argument.

Involving that Prius-type of transmission still seems like a very complicated way to accomplish what could be done with a simple reduction gear and a more powerful electric motor that achieved the same power at lower RPMs with more torque.

Personally, I like the REEV term for the Volt, even if it may not be technically correct. I think it best describes the actual behavior consumers can expect, especially since the term "hybrid" has come to be associated in consumer's mind as an ICE car with an electric motor that sometimes supplements your driving. I have had my Volt since January and found that when people approach me about it (which is frequently), REEV or an EV with a range extending engine, gets the point across to them better than any other language.

I drive Volt #24, my Prius, plug-in since 2004, now sports a Plug-in Conversions kit, and I have driven a pre-production Toyota plug-in Prius. Despite infotainment user interface design issues, my Volt is far and away my favorite car ever, though I drove a BMW 535i for 242,000 miles, a 325i, and a Corvette.
I believe there are a few points I can add to this well-informed discussion:

@priusmaniac,
Yes, your substitution test is one way to test the serial -vs- parallel topology.
The ability to run off of electricity alone is not at test as proven by the Volt.

Ex_EV1, "Involving that Prius-type of transmission still seems like a very complicated way to accomplish what could be done with a simple reduction gear and a more powerful electric motor that achieved the same power at lower RPMs with more torque."
Actually, the Prius has one of the simplest transmissions you can get. It is only gears. No clutches, brakes, or moving parts other than the gears themselves. This is why the Prius (and the similar Ford HEVs) have some of the best quality numbers of all vehicles, hybrid or conventional. In addition, these systems have the capability of operating in both parallel "like" mode as well as series mode depending on how the speed and load of the generator (Sun gear) is controlled. I say "like" because parallel operation can be achieved if you lock up the sun. The Prius does not have a brake on the sun gear (there are designs out there that do, do some patent searches) however the generator can be electrically controlled to near 0 speed, essentially converting this powertrain into a parallel "like" HEV. It can also be run in a series mode by running the motor only (stopping the engine which has a one way clutch to prevent it from spinning backwards) or by running the engine/generator in a charge neutral or charge increase control mode which uses the generator to absorb all of the engine output which is rerouted to either the motor or battery. The biggest downside to this type of trans configuration is the limited torque capability which prevents it from being used on trucks. Other than that, it is one of the simplest, most efficient, most flexible systems out there.
I agree that this system and the Volt are not "pure" parallel or series system but few are. The bigger question is, can these systems at times run in a parallel or series mode. They may not be able at all conditions but in the case of the Volt, 99.9% of driving will be pure series. The Volt may only send mechanical energy to the wheels from the engine only after it 1) uses up the battery reserve and 2) goes above a speed around 70. Until then, it operates as a pure series HEV. I don’t understand what the big deal is with labeling a vehicle "Pure" series or "Pure" Parallel. The fact is, both of these systems (parallel and series) have advantages and disadvantages and any system that is capable of capitalizing on the advantages of both when appropriate is superior in my opinion.

ex-EV1, I think we are on the same page. There are pure series, pure parallel and everything in-between. All those powertrains that are in-between are usually optimized for certain types of driving habits and that is why there is always such passion between different people about why they think one system is better than the other. The reality is that every system is better and worse than the others. There is no one system that works for everyone and that is why there will always be different approaches. The only exception may be the pure BEV but only after the cost comes down and the range gets a little better.