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Discussion Starter · #1 ·
I thought Lithium batteries were about 100 W-hr/lb; which would make the Volt battery about 160 lbs. So why is the curb weight 3780 lbs? That's 300 lbs more than my Mercury Sable Station Wagon!
One suggestion is to minimize the gas engine. Driving at 70 MPH takes about 25 kW (33 HP), so can't I easily run all day with a 40HP engine and 30kW generator? At 54 kW (and 85 HP) it all seems overspec'd by about 100%. How about a new model optimized as a 2nd car for commuting. Then those who commute over 80 miles or absolutely must tow a trailer can get the standard model?
An awesome solution would be to use a small air-cooled motorcycle engine running at 4000 - 8000 RPM; Horsepower = 5252*Torque (ft-lbs) x RPM. Making torque requires more weight (for engine AND generator), so max out the RPM. With a little balancing and a tuned muffler it could be pretty quiet.
With $40,000 invested in this thing I'm glad GM has been so cautious, but after several million customer miles I hope they can lift their restraint a bit and fully realize the benefits of the Volt concept.
 

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I thought Lithium batteries were about 100 W-hr/lb; which would make the Volt battery about 160 lbs. So why is the curb weight 3780 lbs? That's 300 lbs more than my Mercury Sable Station Wagon!
Lots of high strength steel. The Ford Fusion and Lincoln Mk Z hybrids weigh the same, and are only marginally larger. Cars have been getting heavier for years, and as safety standards continue to increase, it's likely that this trend will continue.
 

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Good info from WopOnTour
<snip>
But to better answer your questions, besides the battery the electric motor generator units are not without considerable mass.

MGU-A weighs exactly 51lbs and MGU-B weighs 80lbs. Combined with the final drive unit the total 4ET50 weighs 407lbs soaking wet (inc. 9 quarts of Dexron VI for cooling).There' s also additional coolant for the various systems so there's just under 4 gallons of coolant total on the Volt, about double a typical ICE car.

THEN there's approxmately 25-40% more high strength steel used in Volt, mostly in the floor pan, door sills, pillars, roof rails, and other areas of the car to make it safer by protecting both the occupants AND the Li-Ion battery in the event of a crash.Here's a link to a thread where this is further discussed.
http://gm-volt.com/forum/showthread.php?4939-Volt-Safety-Systems&p=46797#post46797

I've done accident reconstruction during part of my career (technically I'm a "black-box" data analyst and have testified in the courtroom as an "expert" many hundreds of times), and I can tell you you DO NOT want to be T-boned in an older Corolla (especially those pre-dating side impact door bars added about 5 years ago) at any speed much above 30mph, as that puts a new meaning to "reach out and touch someone". They appear to have been made from recycled tin cans. The Volt on the other hand uses top-of-the line "Made in USA" metals and alloys in ALL aspects of it's construction.

Remember weight really isnt as much an issue for EV range as it is for mpg. (rolling resistance and aerodynamic are much more a consideration)
The Nissan Leaf weighs jut a shade over 3500lbs and it doesnt have a range extender!

WopOnTour
 

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The Volt battery weighs over 400 pounds.
 

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Discussion Starter · #6 ·
Correction - Lithium-ion battery weight

Correction: Lithium batteries can give over 100 W-hr per KILOGRAM, not lb.
I thought Lithium batteries were about 100 W-hr/kg; which would make the Volt battery about 160 lbs. So why is the curb weight 3780 lbs? That's 300 lbs more than my Mercury Sable Station Wagon!
One suggestion is to minimize the gas engine. Driving at 70 MPH takes about 25 kW (33 HP), so can't I easily run all day with a 40HP engine and 30kW generator? At 54 kW (and 85 HP) it all seems overspec'd by about 100%. How about a new model optimized as a 2nd car for commuting. Then those who commute over 80 miles or absolutely must tow a trailer can get the standard model?
An awesome solution would be to use a small air-cooled motorcycle engine running at 4000 - 8000 RPM; Horsepower = 5252*Torque (ft-lbs) x RPM. Making torque requires more weight (for engine AND generator), so max out the RPM. With a little balancing and a tuned muffler it could be pretty quiet.
With $40,000 invested in this thing I'm glad GM has been so cautious, but after several million customer miles I hope they can lift their restraint a bit and fully realize the benefits of the Volt concept.
 

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160 kg = 405 pounds. Add in water cooling, insulation, and a steel frame around the battery. I have to believe that nothing was made heavier than neccessary.
 

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I agree, a smaller generator option would be nice. Even though the weight reduction might not help mpg tremendously, for the right person and situation it could work well. Personally, I would feel good about shedding the excess size and weight of generator potential I would rarely need and personally wouldn't mind the louder racing engine trade-off. Of course, other quieter generator options might be possible going forward. :)

However, people's expectations for motor vehicles are so high, at least in the U.S., that this would end up back-firing I'm afraid, what with the "loud" engine going on and off and the inevitable power-fade situation when some unsuspecting owner attempts a long steep grade, this would be smeared all over the media. Pushing a 4000 lb vehicle up a steep grade at 40 HP would really slow down--reminds me of the days my parents drove us over Loveland pass in Colorado in our loaded VW bus!

At this point in time it would just cause a black eye on the Volt and EREVs in general, unfortunately. Perhaps another super-econo-EREV model would be appropriate for this kind of thing where consumer expectations are lower.
 

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Four hundred pounds reduces the EV range by one mile on the Highway Cycle and by two miles on the City Cycle. Who cares? For an ICE car mass is the big issue. For EVs it's an issue but not as big as aerodynamics or ancillary loads. The more you know about EVs the more likely you are to bring up the CdA or the HVAC system and the less likely you are to bring up mass.
 

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Fisker Karma = 5300 lbs and that is before the owner (or is it owners?) get in.

Now we're talkin' beefy!
 

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3780 lbs is not really heavy for a modern sedan. The Lincoln MKZ I traded on my Volt weighed more, actually, but it was a slightly larger car and had a lot of features (10-way power seats, 4 wh drive) so it is not a good comparison.

What is a good, in fact almost direct comparison, is this: my Volt reminds me very much of the Audi A4 I had before the Lincoln: its almost exactly the same size inside and out, feels and drives just about the same. That A4 weighed 3710 lbs with the turbo four and tiptronic transmission so the Volt is not that much heavier. Both feel equally solid and well built. The Audi was a bit faster zero to 60 than the Volt, but the Volt is more responsive in traffic and around town, so I think acceleration is a wash, while the Volt handles and feels as good to drive as the Audi did (the nearly neutral handling in turns under power, and the sporty feel are big surprises to me).

So the wieght seems normal to me . . .
 

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Discussion Starter · #12 ·
Not the Batteries; It's the ICE/GenSet

Lot's of good input from the Experts; Thanks! 80 lbs for a 160-HP electric motor is impressive, and 88 W-hrs/kg on the battery is very good too, almost 3 times better than lead-acid, especially if this includes the racks and temp controls. But the main focus of my opening comment is that the 1400cc 85-HP engine (260 lbs, wet?) and 54 kWatt generator (51-lbs) is overkill. An optional 35-HP gen-set would be fine for alot of buyers (especially those who are opting for the Nissan Leaf due to cost). So, make it two options, priced accordingly.

"Remember weight really isn't as much an issue for EV range as it is for mpg." Don't know where that came from? Weight has always been recognized as a major factor in fuel (or charge) economy. I agree that air resistance is the same for a heavier model but not true for rolling resistance force (RRF), which is the product of the RR coefficient (RRC) times weight. Also the energy required to accelerate is a function of weight (1/2 mv^2), and the percent lost (not recovered by regen) is your main cost for getting from one traffic light to the next. So, at speeds below 55 mph weight is the major factor affecting battery range and still very significant at 80 mph.

To me, an optional air-cooled, high RPM, 36kW gen-set (probably under 80-lbs) is very appealing? 2013 model?
 

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But the main focus of my opening comment is that the 1400cc 85-HP engine (260 lbs, wet?) and 54 kWatt generator (51-lbs) is overkill.

To me, an optional air-cooled, high RPM, 36kW gen-set (probably under 80-lbs) is very appealing? 2013 model?
MG A is also part of the Volt's highway cruising strategy - based on comparison with the Leaf and the SAE papers, those ~50 pounds buy ~10% better efficiency at highway speeds - worth the tradeoff in my book.

GM said that the engine "adds 140 pounds." I'm not sure if that means the block weighs that, or the total all up weight impact is 140 pounds. I'm guessing the former. I am curious where you think you can get an air cooled 36 kW genset that meets EPA SULEV or better and is under 80 pounds. Actually, I don't think you can get a conventional ICE that meets emissions and delivers that power in that weight, without the generator.

Also note in passing that air cooled engines generally have substantially worse economy, and by separating the Voltec into a pure series powertrain you lose another ~10% from generator losses at freeway speeds. Since the putative goal of this exercise was improved efficiency, I think you're going about it the wrong way.

The only way to get the kind of power to weight ratio you're suggesting with good efficiency and within emissions that I know of is a gas turbine - like the C-X75 prototype. Even then, the reduced efficiency of pure series will likely mean similar overall fuel economy.

If you want the ultimate in efficiency for CS for the future, it'd be either a diesel Voltec approach (I don't know that GM has a suitable candidate, but the VW 1.2L and 1.4L or possibly the M-B 1.0L from the smart car are the right size/power range) or possibly a fuel cell if they get more practical in the next few years.

(the BSFC chart for the Volt posted here has a minimum consumption per kWh 20% higher than the 1.9L TDI VW. I don't have a bsfc chart for the 1.4L or 1.2L handy, but I think they do better yet.)
 

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I'm not comparing the Volt with a big V-6 driven Mercury. This is a new world, with new technology. Let's compare it to the PML Mini-Cooper ( http://www.youtube.com/watch?v=W0Sy7XnJBPE ). Compare it against what is now possible, not against what we've had for the last 50 years.
Interesting! Hopefully they can deliver on their goals. Bright outlook indeed if they suceed. :D
 

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A small, light, high rpm high performance engine is going to wear out a heck of a lot quicker and get GM a bad rap for making crap. Piston miles are piston miles, more turns per mile down the road = shorter life, period. Ask any motorcycle owner how many 10's of thousands of miles they get between rebuilds (not 100's of thousands!).

That 4 banger is pretty weight optimized (hollow camshafts!), and yes, of course it's 100% overkill - so it can charge batteries AND drive the car in mountain mode. They optimized it for lower RPM than the same thing in the Cruze - which I'd bet doesn't live as many hours revving like a rice burner in that application (I know, I own one of those too). It's a heck of a lot quieter running slow, too.

While yes, weight does increase rolling resistance - better tires mitigate that a lot these days, and you do get it back in regen, largely. My 200 mpg ICE gokart does well by being super light - but in a head on collision with a dog, you're dead - the end. I don't care that it has a chrome-moly roll cage and seatbelts - a human body, no matter how restrained, can only take so many peak G's and things just come apart inside above that.

http://www.coultersmithing.com/OldStuff/kart.html

It's kind of fun to drive when the weather is nice, if you don't mind the noise and all...and I did manage to get it legal on the road, but it's a case of the dancing bear - it can dance, just not very well.
 

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Replace the 12V battery with a racing battery, get rid of the floor mats, change the wheels to lighter ones, go to racing seats and you can save several hundred pounds. Want more? Carbon fiber hood, lose the tire sealant, it will go bad in a couple years anyway. I'm sure there is more to lose, just depends on how light you want to go.
 

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Discussion Starter · #18 ·
Not the Batteries - The ICE.

160 kg = 405 pounds. Add in water cooling, insulation, and a steel frame around the battery. I have to believe that nothing was made heavier than neccessary.
My mistake, 400 lbs for batteries is great. But I believe 85-HP and XXX lbs for the 1400 cc engine is the main target to lighten up this vehicle. The new Chevy Sail has either a 1200cc or 1400cc as it's only motive power, so why have a gen-set big enough to drive the whole car? There's twice as much generator as needed (i.e. unless you need to drive 120 mph for 2 hours straight, so Germans might want to keep this, but let's make it an option). The generator was an ultra-conservative choice, proven engine (I think it was originally in the Opel Kaddett), quiet, can run at low RPM, etc. But let's push the envelope in the coming years. I think the Volt could easily drop 300 lbs, then you could move the cabin forward and give more legroom, which may be what GM did for the Cadillac ELS, which is based on a Volt chassis. This would all give some better performance, which you might expect in a Cadillac. The other heavy parts are the windshield and liftgate window, any new technologies to help here?
 

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My mistake, 400 lbs for batteries is great. But I believe 85-HP and XXX lbs for the 1400 cc engine is the main target to lighten up this vehicle. The new Chevy Sail has either a 1200cc or 1400cc as it's only motive power, so why have a gen-set big enough to drive the whole car? There's twice as much generator as needed (i.e. unless you need to drive 120 mph for 2 hours straight, so Germans might want to keep this, but let's make it an option). The generator was an ultra-conservative choice, proven engine (I think it was originally in the Opel Kaddett), quiet, can run at low RPM, etc. But let's push the envelope in the coming years. I think the Volt could easily drop 300 lbs, then you could move the cabin forward and give more legroom, which may be what GM did for the Cadillac ELS, which is based on a Volt chassis. This would all give some better performance, which you might expect in a Cadillac. The other heavy parts are the windshield and liftgate window, any new technologies to help here?
It's actually simple physics Doc.
The Volt's ICE ICE is sized to match its electrical generation requirements. You simply cannot produce 55kw of peak power ( approximately 74HP) with anything LESS than 55kw/75hp without contravening those laws of physics! So step 1 would be an engine of 74HP minimum.

THEN, you then must also account for any efficiencies and losses in the mechanical to electrical conversions and come up with an ICE capable of doing the job. Believe me to keep these inefficiencies to <10% was/is considered a huge engineering accomplishment! (and a tribute to the Volts motor generator A construction and power electronics design) So in case of the Volt the 60kw (~80 hp) 1.4L Family 0 ICE would represent the most closely matched horses available in the stable to achieve these goals power wise.

While there might be a few opportunities for weight savings here, they wouldn’t be that significant. Just trying to find another 80hp engine that weighs significantly less wouldn’t be easy without going to something whimsical like turbines or some other unproven technology. Even atttmpting to use other newer ICE technologies such as direct injection or HCCI wasnt worth the additional costs or risks IMHO. In future iterations perhaps...

Besides, from an engineering perspective curb weight really isn’t as significant in an EV as you appear to be making it out to be and simply comparing it to a crap-can Sable wagon makes absolutely no sense at all.
When comparing the Volt to other EVs and even many hybrids it is clearly "within acceptable parameters" .
You being a doctor and all should be quite familiar those terms such as those. (think blood test results etc.) LOL

WopOnTour
 

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It's actually simple physics Doc.
The Volt's ICE ICE is sized to match its electrical generation requirements. You simply cannot produce 55kw of peak power ( approximately 74HP) with anything LESS than 55kw/75hp without contravening those laws of physics! So step 1 would be an engine of 74HP minimum.
The only part I'm not quite clear on is where the 55kW requirement came from. MG A on the Volt (and I believe on the FWD Two-mode Hybrid it shares transmission bits with) is 55kW, presumably for the same reason.

The discussion in the forum is that all you'd really need is an engine to match or slightly exceed your long period base load in highway driving (20kW?) Of course, that'd involve a different usage strategy - from what I've seen the Volt doesn't allow much battery range while in charge sustaining - it seems to have a ~500 Wh window, and only ~150 Wh below the nominal SoC set point.

To make a smaller engine work, you'd have to allow much more battery cycling for acceleration and hills (and therefore go to CS at a higher SoC?)

If you can, how did GM develop the 55kW requirement?
 
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