GM Volt Forum banner

Heavier than my Mercury Station Wagon? Yikes!

11K views 39 replies 18 participants last post by  Dr Mark 
#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.
 
#2 ·
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.
 
#3 ·
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
 
#4 ·
The Volt battery weighs over 400 pounds.
 
#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.
 
#18 ·
Not the Batteries - The ICE.



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?
 
#19 · (Edited)
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
 
#20 ·
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?
 
#8 ·
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.
 
#9 ·
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.
 
#23 ·
Four hundred pounds reduces the EV range by one mile on the Highway Cycle and by two miles on the City Cycle.
My Freshman Physics professor taught me to use the Gadonkin Experiment, which evaluates the effect of an experimental factor by exagerating it; for instance, Newton proved that objects of different mass fall at the same rate, but that rule ignores air resistance; so WITH air resistance, does a cannon ball fired straight up take longer going up, or coming down? A Gadonkin Experiment would be to fire a feather from a cannon, since that maximizes the air resistance factor. Now your mind can envision that it would go up faster and float on the way down (shortens the up time and lengthens the down time). For our problem, to evaluate weight, take city driving where air resistance is minimal. Gadonkin would say, "then if we drop 4000lbs, at 2 MPG per 400 lbs, we'd only get 55 MPG; Does that seem reasonable to push around NOTHING". So I'm suspicious of your figures. Maybe you'll say "But it's non-linear, you can't go all the way to zero weight". But rolling resistance force (RRF = RRC * Weight) and acceleration force (Mass * Acceleration) ARE both linear with weight, all the way to 0 lbs; so half the weight should give double the miles (or 400 lbs = ~ 4 MPG)". Why doesn't your MPG calculation go to infinity at zero weight? Remember, the Saturn SL2 was only 2400 lbs and had a 5 star crash rating. Let's lose some pounds.
 
#10 · (Edited)
Fisker Karma = 5300 lbs and that is before the owner (or is it owners?) get in.

Now we're talkin' beefy!
 
#11 ·
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 . . .
 
#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?
 
#14 ·
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.)
 
#16 ·
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.
 
#25 ·
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!)
Again, I'm only advocating the smaller engine for customers who have a second car (for long trips over the Rocky Mountains) and want to make the Volt their commuter car. In that case, the engine would be used for maybe 10% of the miles driven, so a standard 100,000 mile engine would be good for 1 MILLION Volt miles. Is the rest of the car design for 1,000,000 miles? Also note that the 1400cc ICE is run under controlled conditions so it is never abused or strained. The ICE in the PML Mini-Cooper project with in-wheel motors (referenced 2 weeks ago) was a 25HP Kawasaki Ninja engine, so road certification as an ICE should be possible.
 
#17 ·
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.
 
#26 ·
"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." You missed my point WopOnTour, which is, Not everyone needs to generate 55kW. That requirement is for climbing the Rocky Mountains (70mph sustained, up a 6% grade). If you own a second car for that kind of trip, and especially if you live in Oklahoma, Texas, Florida (any of the South), and especially if you want the Volt mainly as a commuting car, you could downsize the generator to 30 kW, and THEN a 40-HP ICE would be sufficient. I'd very much like to see what improvements in 0-60 time, MPG, M/kW-hr etc and purchase price this would allow. BUT, only as an option. Some people DO need to climb the Rocky Mountains every weekend, or even every day, and the big engine is the right solution. And, of course, for those who chose the lower power option, they better not complain when they have to stop in Idaho Springs, CO for lunch and let the Volt recharge itself.
 
#27 ·
I thought Lithium batteries were about 100 W-hr/lb; which would make the Volt battery about 160 lbs.
Your assumption is wrong. Not all Lithium battery chemistry has the same energy density. Lithium batteries used in vehicles have to survive thousands of recharge cycles and be non-flamible. The Volt battery weighs in at about 400 lbs including the enclosure and internal cooling system.
 
#31 · (Edited)
Figured I'd add a little data to the discussion (though its pretty far from the thread topic). The power demand
for 55mph at a 6% grade is 48kw, 75mph at a 0% grade is about the same. 85mph I think more like 52kw, depending on wind load, rolling resistance, etc).


Consider the following figure


which is from http://www.transportation.anl.gov/pdfs/HV/551.pdf
which is from an Argonne lab report.

So while people in FL may not need MM, they may still need 50KW if they drive fast.
(I think this data the LA92 loop data.)
 

Attachments

#32 ·
The power demand for 55mph at a 6% grade is 48kw, 75mph at a 0% grade is about the same.
Good point! Next time I'm in west Texas or southern Utah (80 MPH speed limits) I'll have to DashDAQ the power draw (or if I can sneak out to a lonely stretch of desert road...). It'd be interesting to know what the maximum flat level sustained speed is. If your numbers are correct it'd be less then 101 MPH so it's definitely something to check. I know it's greater then 80 MPH.

I suspect the Argonne graph you reference is non-sequitur. If I read the report correctly it's based on the analysis of ">110 Trips One day in Kansas City" (page 28). It's certainly not based on LA92 or US06, because of the presence of the 90 and 100 MPH histogram bucket hits. I think it's also based on a mapping of conventional vehicles (page 30) applied to theoretical BEV/PHEV performances. So YkWMV!
 
#35 ·
It's not 85%, not anymore. The Volt's 1.4L engine converts 33% of the heat energy generated by burning gasoline into mechanical motion (33% thermal efficiency) in the peak range (which is where it operates *most* of the time when in CS mode.) The rest is lost as heat, in at least three directions - into the oil, into the coolant, and out the exhaust pipe.

The oil and water are sufficiently low grade heat (low differential from ambient temperature) it's doubtful that any attempt to recover them would be practical from a cost or weight standpoint.

The 40%? that goes out the exhaust might be possible. Beyond dissimilar exhaust strokes (Atkinson cycle design, which the Volt emulates in certain regimes we're told,) your most likely options would be a turbine in the exhaust stream (either turbo-compounding, like in certain large radial aircraft engines in the late 40s, or connected to an electric generator,) or a heat exchanger in the exhaust to drive a stirling-cycle device.

The Stirling idea I kinda like, but I'm still not sure it's practical - I'm not sure you can extract enough power to balance the weight you're carrying, let alone the cost - especially in an EREV where you're only using the engine 30% of the time.
 
#36 ·
Reading another post today I realize someone had done some measurements.
This thread
http://gm-volt.com/forum/showthread.php?8235-MPGe-at-Various-Speeds
Had measurements by honoreitiscom on a Volt which yielded following chart

which shows .4kw/m at 75mph so sustained that is only 30kwh.
At 70mph its about 24kw. at 65 its about 20kw.
The energy demands from wind increase super-linearly. By 85mph it would be over 40.

However, all the above is EV mode, not CS mode could be a little different.
 
#37 · (Edited)
However, all the above is EV mode, not CS mode could be a little different.
Well, the power requirements should be the same. The efficiency in achieving them might not be. You could even end up with something as confused as Car and Driver, who, presumably because they didn't realize that the Volt does long term power cycles at lower speeds in CS mode, thought it was more efficient to drive at 70 than at 40:

http://www.caranddriver.com/compari...t-vs-2011-chevrolet-cruze-eco-comparison-test

Note the graph of "steady state MPG" they included near the bottom of the article...

honoreitiscom's data is interesting. It suggests a floor of around 200-210 Wh/mile in the climate/configuration he tested in, and rises with the velocity squared curve that is to be expected from aerodynamic drive. Due to fixed parasitic loads, the Wh/mile consumption will also go up if you keep testing to slow enough speeds.

This also suggests that the maximum speed case may be the limiting case. If you assume (conservative/worst case assumption) that all load from 75 mph increases with velocity squared like drag, then doubling the power to 60kW would increase the speed by 41% - 75*1.41= 105.75 (actually we only have 55 kW - the square root of 55/30=1.833 is 1.354 times 75 is 101.5 mph) While the loads are drag dominated, there are certainly some non-aerodynamic loads which stay constant or increase linearly involved, but I find the close agreement interesting...
 
#38 ·
Can't believe that city driving number.

Tire friction is rolling resistance coefficient (RRC) * mass = RR Force, and the acceleration-deceleration loss = (1 - Generator Efficiency)*(1-Motor Efficiency)* integral of (Force * ds), where ds is a differential distance. As we know F = ma, so the force you're integrating is also linearly proportional to the vehicle mass. Summary: The major losses at low speed are linear with weight, which means losing 400lbs should cut 10% in expended energy, which is 4 to 4.5 miles, not 2.

The more you know about Physics, the more you'll be concerned with weight!
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top