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Old 01-07-2007, 10:02 AM   #11
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Quote:
Originally Posted by red91sit
wouldn't it be FAR more efficent if it was connected to the wheels?
But then they'd have to engineer a torque-splitting device (transmission) that didn't infringe on Toyota's brilliant system and patents (which so far 2 other manufacturers - Ford and Nissan - have licensed, rather than try to invent their own flavour of the same thing).

I think that's one reason GM is avoiding the parallel approach. Also, it gives them much greater packaging flexibility.
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Old 01-07-2007, 10:34 AM   #12
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Quote:
Originally Posted by red91sit
I'm also confused by this. The little motor does make 207 lb/ft of torque, but wouldn't it be FAR more efficent if it was connected to the wheels? Then it could maintaing near W.O.T. to charge the batteries and move the vehicle until the batteries are full charged then it turns off until say 50% S.O.C.

Right now that little motor has to go through all of these reactions
(gas)chemical->
(engine) mechanical->
(generator) electrical->
(battery) chemical->
(motor) electrical->
(wheels) mechanical

that has to suck the efficeincy right out the window.
Maybe ... it's a trade off. The ICE is run at 1800 rpm because that's probably where it's the most efficient in terms of hp / gallon of gas.

If you start connecting the ICE to wheels through clutches, torque converters, gears, etc., you lose a lot to mechanical friction. You also have to vary the speed of the engine and depart it's peak efficiency range for most of the time. If the average ICE-powered drive train attains the efficiency of ~15%, and if you could make the engine use gas at say 30% efficency because it stays at its best speed when in use, you'll have gained 100%. I don't now how accurate those numbers are, but Toecutter can probably straighten me out. The rest if the losses are taken from there.

Edit: ok, maybe an ICE-driven vehidle is only 12.6% efficient.

Also the complexity (thanks Darin) required to have the ICE do both jobs also becomes a barrier. I still can't figure out how all the modes of the Pruis work with all of its motors and planetary gears. Besides, the Prius still can't run exclusively off of the grid (as an alternate form of energy) w/o some pretty expensive mods, so it's still not complex enough.

ICE designs usually have to be way over-powered because the time when you need to get the most power out of the engine is when it has the least torque and is very inefficient: accelerating from a stop. At cruise, the car needs only between 5 and 20 hp to make it's way down the road depending on the car and speed. On average that 71 hp engine probably puts out twice what the car needs. That's why it only has to run half the time to keep up with the battery drain - and the ICE is off the rest of the time. Electric motors, OTOH, have their highest torque from start and so are ideal for the job of moving a car.
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Old 01-07-2007, 10:39 AM   #13
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Originally Posted by MetroMPG
I think that's one reason GM is avoiding the parallel approach. Also, it gives them much greater packaging flexibility.
I figure the likelihood of exterior design changes is proportional to that packaging flexiblity ... and that's a very good thing.
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Old 01-07-2007, 12:40 PM   #14
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The generator needs to be ~80%+ efficient. An off-the-rack model only converts mechanical to electricity at ~50% efficiency, according to most manufacturer stats, so this is crucial for vehicle efficiency. At 80% generator, 40% engine, and 72% battery/inverter/motor, we'd have ~23% vehicle, which is pretty good considering the Prius' efficiency during the EPA highway cycle is only ~20%, and this vehicle would probably have less weight/smaller CoD.
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I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 01-07-2007, 04:12 PM   #15
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As others have asked, when will they build it, how much will it cost, and will it really be as "efficient" as the current "concept car"?

It's not as if this idea is exactly new. Driving wheels using electric motors, and then using fuel to power the generators has been done in the railroad industry for decades now, and it's been talked about as a possibility for normal cars for many years.

As I see it, such an approach has both plusses and minuses vs a more "traditional" design (even a "traditional hybrid design", however much of a misnomer that is), where the ICE directly drives the wheels.

Disadvantages of this design, compared to a more "traditional" design.

Since this design is so "radical" (compared to the ICE/transmission approach we have had for so long), it might take a little while for both the engineering bugs to be worked out, and for it to be built and accepted by the public. The old "chick or the egg" problem, as you ramp up to do something "new".

There are intrinsic inefficiencies with converting mechanical energy into electricity (the "generator") only to immediately convert that electricity back into mechanical work (the electric motor). And these losses are ON TOP OF the losses due to ICE efficiency (which both types of vehicles suffer).

During those times when the ICE is off you are running on batteries. But charging and discharging batteries is also not 100%, and so the charge/drain has inefficiencies in storage, in addition to the mechanical=>electric=>mechanical inefficiencies mentioned above.

And when you don't have the ICE on, you are also not generating heat. This could be a problem in the winter. I suppose you could get around this by either: A) Have a supplemental electrical heater for the passengers, and/or B) Run the ICE some when you need "waste heat". But either option is not without its costs. The supplemental heater will add some cost/complexity to the system, and will also use electricity (and electric heating isn't exactly "efficient"). And running the ICE to generating heat will obviously use some gas (although it would also generate electricity at the same time, so it's not just using gas for heat).

OTOH I also see several advantages to this approach:

It is MUCH simpler from an engineering standpoint! This (in theory) makes the design costs for such a vehicle much lower. It should also make it easier/cheaper for DIY upgrades/changes.

Such a vehicle should have less weight (and less weight does help FE) than a (plug-in) hybrid using a more "traditional" design, as you (potentially) avoid a lot of heavy mechanical parts (drive train, transmission, etc). Instead, such a vehicle will have the key sub-systems "loosely" hooked together by a combo of power cables (even very big cables are less heavy than the mechanical linkages) and electrical control signals (very light, and easy to run the wires wherever you need them).

And while there are inefficiencies in converting back and forth between mechanical energy and electricity, there are some inefficiencies in traditional transmissions/drive trains/etc as well. So the "efficiency gap" is not as big as it may at first appear, as you are really only swapping one set of inefficiencies for another (i.e. "pick your poison")...

Because you primarily using the ICE as a "generator", you can optimize the engine to run at the most FE RPMs all the time (instead of designing an engine to give decent torque when you need it). To some degree you get the same effect with a more "traditional" hybrid vehicle (where the electric engines give a decent boost), but with this sort of vehicle you can go all the way to two speed only (efficient run, and full off).

And last (but certainly not least) a vehicle based upon such a "loosely coupled" set of sub-systems really is "flexible" from an engineering/maintenance standpoint (just as the GM marketing folks are saying). The reason is, with a "traditional" vehicle most of the sub-systems are interconnected, so you can't easily upgrade one without touching another. But when you have most of your sub-systems as independent "black boxes", you should be able to easily "mix and match" as you see fit. Got a better power source? Go ahead and swap it in, and other systems (such as the electrical engines driving the wheels) shouldn't care. Ditto for improvements to power storage (better batteries), etc. Want to supplement power with solar cells? Yep that should be easy too. The point is, when you can think of a system as being made up of "independent" plugged together "black boxes", you have a lot of flexibility to improve/replace the innards of those black boxes "one at a time" while still being sure the complete system will work. So it becomes much easier to make "incremental upgrades" to the vehicle, as you can get away with working on a single "black box" (for example, to be more "energy efficient") without worry if that will break some other parts of the system. IMHO this is a HUGE advantage for both vehicle engineers and DIY types (both of which can again start working on the individual pieces as opportunity comes alone, vs having to treat the whole system at once).
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Old 01-07-2007, 07:30 PM   #16
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Quote:
Originally Posted by DracoFelis
As others have asked, when will they build it, how much will it cost, and will it really be as "efficient" as the current "concept car"?
I've lost count how many times I've been suckered into believing GM was finally going to come out with a great product. So far, I have always ended up feeling foolish when I realized it was just their marketeers putting lipstick on the pig again.
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Old 01-07-2007, 08:28 PM   #17
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Green Car Congress has a few more details today.
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Old 01-08-2007, 02:10 AM   #18
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Of course, the achilles heel of the concept is the L-ion pack. Issues of cost and durability of nanotech versions needed to make this a feasible battery remain to be settled.
According to Argonne National Laboratory, in automotive volume, Li Ion battery packs would drop to ~$250/kWh. With mass production, that achilles heel wouldn't exist any longer. This is for 18650s though, which would last about 500 cycles to 100% discharge. With 40 miles all-electric range, life would be an issue for a plug-in hybrid(while a pure EV like the Tesla, pack life > 100,000 miles). The nanobatteries could change this, but as far as I'm concerned, they'ere vaporware until we can see third party testing of an actual product.

Without Altair Nanotechnologies sort of cycle life figures, Li Ion wouldn't be very suitable for a PHEV with low all-electric range. 40 miles range * 500 cycles to 100% = 20,000 miles life. You'd really need 150+ miles range for reasonable battery life to be had on today's 18650s; with range like that, your average discharge would be lower and thus higher cycle life.

The life expectancy issue is probably why Toyota is still using NiMH for its hybrids. Li Ion is currently best suited for long range pure EVs or PHEVs with a long all-electric range.
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Old 01-08-2007, 06:33 AM   #19
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A former GM exec essentially labels the Volt a PR greenwashing exercise:

Quote:
Walter McManus, a former GM executive who is now director of automotive analysis at the University of Michigan, expressed his scepticism that the Volt would ever get to market, and said there were quicker ways for the US car industry to reduce the environmental impact of their products.Raising an eyebrow at what he called "the magic E-Flex", Dr McManus said: "The battery technology that they are depending on is not available yet and just pouring money into it is not going to make it happen. They need to take fuel efficiency more seriously. - source
GM has a poll on their site. 2 questions: would you want them to produce it? Would you buy one?

http://www.gm.com/company/gm_exp_liv...?navID=3.0.1.1
(Opens a Flash widget, the vote link is in top left - "Vote for Volt".)
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Old 01-08-2007, 06:53 AM   #20
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You guys realize that if the tires are 20" tall then the roof is only about 30 inches making it about the height of a Vette - that really cuts down the aero drag frontal area. There are generators out there that are in the 90% efficiency and the battery voltage would be in the 250 - 280 volt range as that is a limit of the electronics that control the power. Using lower voltage would not make sense. Running a turbo is required because you can't naturally asperate 71hp of power burning gas through a 1 liter engine at 1800rpm - there would not be enough air flowing through it - and keeping the RPM low makes it more efficient for sure. Wish we have more definative results on the speed disk hubcaps to conclude on the mag wheels though. Funny thing is I got 50.4mpg yesterday driving back 35 miles from getting gas in my xB.
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