Serial / Series Hybrid Tracker

[dcb]

the thing that makes the volt a good example is that it is still very much the same car, so it is far more an apples to apples comparison than fvt to ??? If series is better than why does the volt need a parallel mode to get better efficiency?

Also you are introducing mpge to the discussion, which is a contentious measure of efficiency.

[NeilBlanchard]

The FVT is a two seat vehicle, so compare it to the Insight?

The Volt is not an ideal series/serial hybrid: it does NOT run in charging mode, but instead varies the RPM to provide power to the motor. It only goes into parallel mode when it needs more torque than the two electric motors can provide, and it weighs a lot more than it should. It is not an optimized EV -- and a good series/serial hybrid has to be an efficient EV.

The Volt uses 176-352wH/mile (8.8kWh / 25-50 miles range), while the eVaro uses 133-160wH/mile (~20kWh / 125-150 miles range). The Volt uses ~8-9 gallons to go 300 miles in charging mode, while the eVaro uses ~2.2 gallons to go 300-375 miles, so if we double that to move 4 people, it is still at least 2X better than the Volt.

Do you see a pattern here?

MPGe is not controversial -- it is repeatable and merely a conversion spreadsheet to compare energy use in various vehicles. We are not comparing carbon used (emissions), just energy used. Besides, the electrical use of the two can be compared, and the ICE mode can be compared separately if you want -- MPGe is just the simplest way to combine everything to a common denominator for an overall comparison.

[cfg83]

Neil -

Originally Posted by NeilBlanchard

...

Series/serial hybrids have several big advantages over pure parallel-only hybrids:

The ICE *should* be run at a single RPM driving a fixed load. (Which is is not how the Volt uses it -- the Volt is not an ideal series/serial implimentation.) This makes several things possible:

This lets the engine be optimized for that one RPM, and we all know that this is ideal situation -- for parallel hybrids, too. (They run best at highway speeds when they don't need to use their transmission.) So, in the case of an Atkinson cycle ICE, this means it can always be at about 38% efficiency.

...

I love the concept of the series-hybrid because of the single-RPM BSFC sweet-spot argument. However, it seems like no one has made one for "normal" 4-wheeled cars. Do you think we could extrapolate the specs of an FVT eVaro into a 4-wheeled 4-passenger equivalent and see what MPGe it gets?

CarloSW2

[NeilBlanchard]

I think 3 vs 4 wheels make virtually zero difference in efficiency. The aero shape (narrow at the back) matters, but the number of wheels is negligible.

[dcb]

Originally Posted by NeilBlanchard

... It only goes into parallel mode when it needs more torque than the two electric motors can provide,...

that isn't what the video said. Not sure where you got that from. I do know it goes out of straight series mode when it wants to be 15% more efficient.

Originally Posted by NeilBlanchard

MPGe is not controversial

it absolutely is, at least around here. Separately listing the energy sources is the only sane way to make sense out of it. If you want to see the electric bias in mpge, look at the all electric wave II which basically was pegged at 190 mpge for the knockout efficiency hiway test. Given the fvt is largely an electric car, it is no suprise that it got good mpge marks. Not a function of series-ness.

The volt is the only apples to apples example out there that I know of. FVT to insight?!? That doesn't make any sense at all. You are saying to compare an xprize trike to a production car and say that this is the basis for saying how great series is? The only thing that changes in the volt is a couple clutches, otherwise it is the same vehicle, thus infinitely less variables than you are trying to introduce.

Originally Posted by NeilBlanchard

I think 3 vs 4 wheels make virtually zero difference in efficiency. The aero shape (narrow at the back) matters, but the number of wheels is negligible.

25% less rotating wheel mass and contact area has to be good for something.

[NeilBlanchard]

Contact pressure/rolling drag is based on weight, not the number of wheels.

The Insight and the eVaro each carry two people and they are the best examples we have of parallel and series/serial hybrids, and this makes them the best concrete way to compare these types of hybrids.

Compare the Volt to what? Comparing it to itself is not a comparison.

Okay, I watched the videos again, and it is used in *reduced* torque demand situations. Look at video #2, especially from 4:00 to the end. The engine does not always engage physically to drive the wheels above 70MPH. This is reiterated in video 3.

I think the biggest improvement in the efficiency is the change in the reduction gear ratio, by driving the the ring gear with the ICE (transmitted through the generator/2nd electric motor), which lowers the RPM of the primary traction motor.

So, they are using the second electric motor, or the ICE to spin the ring gear to reduce the reduction gear ratio, which lowers the RPM of the traction motor -- so they are expending energy to save some energy overall. I would think that a 2-speed transmission or a variable ratio transmission (over a fairly narrow range) would have been a better way to go?

Instead of just changing gears, or adjusting the ratio of the reduction gears, they spin the outer ring gear, which uses power all the time, rather than momentarily.... Sheesh, that doesn't make much sense to this layman!

[NeilBlanchard]

Old thread on series/serial hybrids:

http://ecomodder.com/forum/showthrea...ids-13213.html

[NeilBlanchard]

(click on image for link)

[NeilBlanchard]

Here's a serial hybrid truck, that has been developed by a supermarket chain. They are concerned with efficiency, emissions in congested areas, and with noise.



Here's a brief video (they turn down the music part way through, so you can hear the truck in motion):
http://www.colruytgroup.be/colruytgr...=400&width=500

[NeilBlanchard]

(click on image for link)