Does the Prius have a transmission?

All of which is totally irrelevant to the definition of EREV in the SAE paper.

 

I'm still interested in seeing John's answer to those two questions.

 

You asserted that the definition of EREV somehow changed after the initial Volt rollout. I asked how it changed and what the new definition is.

If I understand you correctly, your answer isn't that GM's definition changed but rather that the definition of EREV is whatever a bunch of commenters on automotive articles and auto forum site posters say it means for the purpose of winning their debates.

These are largely the same folks that think the Volt is almost always operating in series mode when the gas engine is running except under rare conditions at speeds over 70 mph. These people are confused.

Both cars identically fit GM's proposed EREV definition.

Both cars do not start their range extenders based on speed or torque demand. Both cars start off in EV mode when there is usable grid charge left in the battery. Both cars are highway capable by way of the CARB definition when running on battery charge.

 

You are confused.

First, the Volt is an EREV (like the BMW i3) so the gas engine never comes on just because you are climbing a mountain road at high speed and under high power demand. I assume you know this already but I'm repeating it just to be clear for readers.

When the gas engine does start after the usable battery capacity runs empty the Volt operates as a full hybrid with a 0.5 - 1.0 kWh hybrid battery buffer. The gas engine can cycle off if the battery has been recharged enough to drive on electricity temporarily. When the gas engine is running, the Volt can operate either in series mode with the engine only driving a generator to make electricity or it can be in power-split mode where the engine is mechanically clutched to the ring gear of the transaxle where it contributes to driving the wheels.

Anyway, your intuition is completely backwards and this is a common misunderstanding. Under high power (torque demand) as in climbing a mountain or accelerating as quickly as possible the Volt operates in (and will revert to) series mode. It will prefer to use the 150 HP large motor with power coming from the 111 kW capable battery pack and the 55 kW capable gas engine through the generator. On the other hand, the power-split mode happens at lower torque demand and is far more common than series mode in most expressway or highway driving.

The power-split coupling to the planetary ring gear happens frequently and makes a significant contribution to the efficiency of the Volt. It happens more than half the time while the Volt is running through the 2 EPA highway test cycles, for example.

It is coupled like that most of time the gas engine is running at speeds above 36-40 mph with low torque demand (when you aren't accelerating strongly and are maintaining speed on flattish roads).

Specifically, under the US06 EPA highway test cycle, the Volt spends 58% with the gas engine mechanically connected, 16% in series mode with gas engine, 21% with engine off and using one electric motor, and 5% with engine off and using the two electric motors combined.

US06 includes a bunch of starts and stops at the beginning and end of the test cycle which accounts for the time spent without the gas engine mechanically connected. The older, less aggressive, and freer-flowing HWFET highway cycle almost certainly spends even more time with the gas engine coupled although I haven't seen the numbers.

So, again, series mode is used for speeds under 36 or so mph and during high torque demand. Power split mode is used the rest of the time the gas engine is running because it is more efficient at speeds above 35-40 mph.

The Volt has an engine maintenance mode which ensures that the engine is started and brought up to its full operating temperature at least once every 6 weeks regardless of miles driven. This keeps the engine lubricated and burns off any moisture condensation which may have built up.

Separately, the Volt has a fuel maintenance mode which ensures that the average age of the gasoline in the tank is less than 12 months. If needed, it will force the Volt to burn gas in hybrid mode until you put in enough fresh gas.

 

The Volt's fuel maintenance mode is for extreme outliers to prevent them from getting stale gas that won't burn well or gunks up their fuel lines. Almost nobody runs into fuel maintenance. It's a cause for bragging rights for the very few owners who run into it.

If you drove an average 12,000 miles a year and you kept a half-tank (4.6 gallons) of gasoline in the car you would have to average at least 2,600 mpg during the entire year in order to have any gasoline remaining that would be considered stale.

 

That's a common misunderstanding due to poor initial media reporting which then was cited by Wikipedia which was then used as background source material for newer media reports...

Please reread what I wrote earlier.

The data I quoted about how often the engine has a mechanical path to the wheels (power-split mode) during the EPA highway test cycle US06 is from an SAE paper written by the GM engineers that designed the Volt transmission.

They found that power-split mode with the gas engine running was taking 58% of the total vs. 16% for series mode. In other words, power-split was 3.6 times as likely as series mode when driving down the highway using that test.

The data is from:
The GM “Voltec” 4ET50 Multi-Mode Electric Transaxle

You can see a summary of the paper and some selected graphs at the link below but note that the speeds are in metric:

Transmission thread at GM-Volt.com

The GM video you linked to does not show what you think it shows. It merely shows the different clutching modes and uses an example speed of 70 mph for switching from series to power-split mode. They never said 70 mph was a magic speed at which power-split is enabled but some people have assumed that it was. I'm not saying anything that conflicts with the video.

The flaw in the video is that it is unclear that power-split with the gas engine connected to the generator and ring gear is common at much lower speeds than 70 mph. It also does not describe what happens if you are cruising on the highway in power-split mode at 60 mph and stomp on the accelerator to pass a slower vehicle. Modest acceleration or hill climbing such as the overpass example in the video will stay in power-split but stomping on the accelerator will generally cause the Volt to revert from power-split back to series mode -- which is the opposite of what you said.

 

What about the graphs from the SAE technical report written by GM engineers I linked to on the GM-Volt.com thread?

The fact that the Volt frequently operates on power-split mode when the gas engine is running has nothing at all to do with the Volts behavior as an EV when the battery still has usable charge left. When there is usable charge the gas engine will never run due to speed or power requirements.

 

It's available for $22 or so online but you would have to be really interested to pay that much.

But you've read it! Did I misrepresent anything in my summary of the paper?

The relevant graphs from the paper are freely viewable at the GM-Volt.com link I posted earlier and they alone clearly show power-split mode being used at lower torque demand levels when the gas engine is running at speeds as low as 36 mph (around 60 kph on the graph in metric).

Here's the link again:

SAE Volt Transaxle Graphs at GM-Volt.com