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Old 10-12-2010, 05:25 PM   #1 (permalink)
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Serial / Series Hybrid Tracker

Here's a list of serial / series hybrid generators (aka range extender, aka EREV aka REEV):

Lotus:

GETRAG serial / parallel:

FEV has two: Green Car Congress: FEV, Inc. Develops 40kW Range Extender Unit


FVT:

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Old 10-13-2010, 08:40 AM   #2 (permalink)
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Capstone C30 turbine genset:



Chevrolet Volt (serial / part time parallel):

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Old 11-01-2010, 11:45 PM   #3 (permalink)
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Here's a different take on a serial hybrid:

Company Announces Diesel-Powered, Range Extending, Towable Trailer for Electric Cars | PluginCars.com

It has been done before, but this is company that intends to build 'em.
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Old 11-02-2010, 12:03 PM   #4 (permalink)
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There are "obvious" losses in any drivetrain. But, EV's are by far better than ICE's in most driving situations. Only steady-state highway speeds are better in an ICE, and not coincidentally, a series/serial hybrid mimics an ICE on the highway; but it does so ALL THE TIME. So, the actual drive motor is electric which is much better in most situations, and when the ICE is needed, it runs in it's ideal conditions.

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.

This reduces the required displacement and reduces the maximum torque, because the battery can be used as buffer, and only has to meet the average power level.

This reduces the weight of the engine, it's cooling system, the size of the fuel tank.

There is no multi-ratio transmission -- so less weight again. The need for a transmission is an engineering compromise -- the engine cannot meet the torque requirements, and it must be run at all sorts of off-peak conditions.

There is no idling the ICE; by definition, if it running it will be running at it peak efficiency actually doing work at all times when it is running. If you add a stop/start, then this is more complex.

You do not *need* to run the ICE when running at highway speeds, as you would in a true "Parallel-only" hybrid. So for short drives that under the range of the battery, the ICE never comes on.

If you are on a long drive with a lot of it at slow speeds, you cannot extend the range of electric-only mode. So, the ICE cannot contribute if the battery is depleted, and the driving needed is slower than where the engine can be used.

The ICE engine can be located in the car independent of the drivetrain; since there is no mechanical connections to the drive wheels.

Both series/serial hybrids have regenerative braking, and that's a good thing. Both types also run the ICE in it ideal mode, though on a parallel hybrid, the load is only constant on flat ground and no gusting winds. And the speed of the vehicle has to be linked to the ICE's RPM, in order for it to be peak efficiency, so this limits it's flexibility.

Parallel hybrids are more difficult to build: either they drive the rear wheels, while the electric motor drives the front (for better regen), or there needs to be a additional drive wheel. In a parallel hybrid, the ICE must be located to make the best connection the drive wheels, and this means it cannot necessarily be located for best cooling aerodynamics or weight distribution. The GM Precept is the only design I can think of that is a true parallel-only design, and they have a transmission on the ICE, and the ICE is in the back, making cooling more difficult and limiting the storage.



The "fifth" wheel type of parallel hybrid is even harder in many ways. It is aerodynamically and mechanically challenging. Lowering/Lifting the wheel needs to be figured out...

Both of these types of parallel-only setups require a second mechanical drivetrain, adding weight.

If the both the electric and the ICE motors drive the front wheels, then this adds a transmission and a clutch, and a more complex control system.

*******

In a nutshell, a series/serial hybrid has all the advantages of an EV, and uses the ICE at it's best RPM, and the ICE can be smaller, with all the related weight savings.

A true parallel-only hybrid is harder to implement, and is less flexible in the type of driving, and in it's physical set up. So, while it may have theoretical efficiency advantage (at a particular speed on flat ground and no gusting winds), I think if you cannot have the pure EV range (which is by far the best in most situations), then a range extending series/serial genset extends the advantage of the EV better.

The new NBM "Hummingbird" batteries might make the need for hybrids moot.

Edit: The X-Prize Knockout Round is important to consider.

The average of the 6 hybrids that used their ICE's during the contest (which did not including the FVT) was 61.26MPGe Please note, these are all parallel hybrids.

The average of the 5 internal combustion drive cars was 82.92MPGe.

The average of the 12 vehicles using electric drive MPGe (I'm including the FVT in this) was 134.7MPGe.

So the lowest MPGe of an electric drive; the AMP'd Sky was 86.7MPGe (Tango was 86.8), while the best of a car with an internal combustion is the Edison2 #97 at 101.4. (Actually, the FVT has a ICE powered generator onboard, but did not need it *at all* in the X-Prize. It would be great to see how the eVaro does for MPGe in charging mode!) The hybrids all were all below the 67MPGe -- except the WWU at 92.5 (and the FVT).

The FVT got 152.5MPGe while carrying the weight of the genset, and the genset would have to be pretty horrible to lower the average MPGe to below the WWU, which was by far the best hybrid -- and it (the WWU) was a EV drivetrain combined with an Insight drivetrain; so it was a parallel hybrid/parallel hybrid hybrid, so-to-speak.
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Old 11-03-2010, 07:01 AM   #5 (permalink)
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Dude, do an accounting of the losses of a series drivetrain, just once, without the rose colored glasses. The "efficiency envelope" for an ICE is also much larger than steady state cruise. This seems like a very unbalanced viewpoint you have.

Yes all drivetrains have losses, but driving the wheels directly gives the volt a 15% boost in efficiency, so that should be a clue as to how sloppy series is.
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Old 11-03-2010, 08:26 AM   #6 (permalink)
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Series/serial hybrids are essentially EV's, with a generator onboard. They beat parallel hybrids easily in efficiency -- look at the X-Prize data.

What have I said that is incorrect?
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Old 11-03-2010, 08:46 AM   #7 (permalink)
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Quote:
Originally Posted by NeilBlanchard View Post
Series/serial hybrids are essentially EV's, with a generator onboard. They beat parallel hybrids easily in efficiency -- look at the X-Prize data.

What have I said that is incorrect?
Hybrids did a big fail in the xprize.

"They beat parallel hybrids easily in efficiency" is completely unfounded. You have absolutely no data to back that up. I think it is irresponsible.
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Old 11-03-2010, 10:53 AM   #8 (permalink)
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I think this comes down to if you are assuming stupid drivers or smart ones.

If I know I have to go 300 miles, and I have X battery charge and Y gallons of gas, and a few gears to choose from, I know for 100% certain that I can get to my destination with much less gas by using the engine to drive the wheels when it makes sense (i.e. when I can hold it within %85 of bsfc peak, which is almost 100% of the time), than I can by using the engine to drive a generator with a fixed 15% loss.

I also think it is a mistake to cater to stupid drivers, as you only breed more stupid drivers. Think of how many folks can't even drive a stick shift now.
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Old 11-03-2010, 11:45 AM   #9 (permalink)
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The speed you can drive ultimately is determined by the roads you are driving on, the conditions (weather, etc.), traffic, etc., and if you are required to go slow at the beginning, and at the end of the drive, then a parallel hybrid won't help you go slow once the battery is depleted.

The FVT eVaro has a 22kWh battery and a 1100cc 20kW genset with a 2.2 gallon gasoline tank. It goes 125-150 miles in EV mode, and in charging mode it can go another 300-375 miles. So, if it uses ~20kWh of electricity and 2.2 gallons to go a total of ~425-525 miles, using the X-Prize spreadsheet, that is 152-188MPGe average.

The battery holds usable energy equivalent to 0.58 gallons of gasoline.



The electric only energy use is ~213-255MPGe. During the charging mode, that is 136-170MPGe. Those are the performance numbers; not theoretical mathematics.

So, the charging mode is 20-47% lower efficiency than in EV mode. That difference would be combination of the engine and generator efficiency; since the electric motor is in both sides of the equation.

++++++++

Do you have a real world example of a parallel hybrid performance?

The only one I can think of is the original Honda Insight.
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Old 11-03-2010, 11:59 AM   #10 (permalink)
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Quote:
Originally Posted by NeilBlanchard View Post
The speed you can drive ultimately is determined by the roads you are driving on, the conditions (weather, etc.), traffic, etc., and if you are required to go slow at the beginning, and at the end of the drive, then a parallel hybrid won't help you go slow once the battery is depleted....
Again, a smart driver can compensate for this quite adequately, especially if given some gears to choose from, by managing the different energy stores.

Say I am going on my 300 mile trip, I putter around on battery till I get to the hiway, then I stop using the battery excepting for keeping the lights on, and leave myself sufficient reserves to get to my destination charging station when I get off the hiway again. What I am assuming is that the driver has complete control over when to use electricity or gas or both and can make the appropriate decisions based on knowledge the car does not have.

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