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GM Provides Snapshot of State of the Volt; Tracking to Production in Nov 2010
4 April 2008
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| The T-shaped Li-ion packs undergoing cycle testing in the battery laboratory in Michigan. The pack from Continental/A123Systems is on the left; the pack from CPI is on the right. The slot in the middle of each pack is to accommodate a structural beam that runs across the breadth of the car. Click to enlarge. |
In a day-long briefing at the GM Tech Center in Warren, Michigan, the GM team responsible for the Volt provided a snapshot of the current state of development of the extended range electric vehicle (earlier post)—which is tracking to production in November 2010—to an international group of journalists.
The accelerated development of the Volt is pushing GM to design, to develop and to test in parallel the powertrain and the vehicle. Key topics addressed during the briefing were the cycle life and calendar life testing of the lithium-ion battery pack; the coming integration this month of the first packs into the mules; other powertrain and exhaust system issues; aerodynamic modifications to support the 40 mile all-electric range; and design issues.
The battery packs and the powertrain. GM has received initial packs from both CPI and A123Systems. General parameters of the packs are an energy capacity of 16 kWh; weight of about 170 kg, length of about 1.8m. The packs, which are based on prismatic cells from each company (the prismatic cell is GM’s go-forward design choice for energy batteries and perhaps even power batteries, according to Denise Gray, Energy Storage Devices and Strategies Director) need to:
Provide sufficient power to accelerate the vehicle from 0 to 60 in 8.5 seconds; deliver passing capability; and deliver “predicted driveability”.
Provide sufficient energy to support a 40-mile all electric range under city and highway driving conditions.
Have a cycle life that supports 150,000 miles under mixed electric vehicle (EV) charge depleting and extended range (ER) charge sustaining modes of operation.
Have a calendar life that is more than 10 years under real world conditions.
GM and its suppliers have already undertaken the cell level testing that has assessed the capability of each type of cell (CPI uses a manganese spinel chemistry, A123Systems a nano-phosphate chemistry) to achieve the required vehicle performance along with accelerated life testing and abuse behavior.
GM is currently engaged in pack level testing (cycle life, calendar life, temperature and vibration). The third major test set will be the dynamic testing of the packs in the mules and then in the production version of the Volt under road conditions.
GM also plans to test charge integration under a variety of simulated conditions (110V, 220V, presence of appliances such as washer/dryer or freezer in the garage, etc.), brownouts, blackouts, and so on.
The dynamic testing will begin following the integration of the first packs into E-flex mules (based on the Malibu) later this month. That will proceed in parallel with the pack-level tests in the battery lab that will continue for almost two more years—the shortest amount of time into which GM could compress testing to validate the required 10-year, 150,000-mile lifespan of the packs.
| GM’s Cycle Test for the Volt Packs | ||||||
|---|---|---|---|---|---|---|
| Mode | Cycle | Time | Miles | Cum. Miles | ||
| EV | Urban | 23 min. | 7.5 | 7.5 | ||
| EV | US06 | 10 min. | 8.0 | 15.5 | ||
| EV | Hwy. | 13 min. | 10.1 | 25.6 | ||
| EV | Urban | 23 min. | 7.5 | 33.1 | ||
| EV | Urban | 23 min. | 7.5 | 40.6 | ||
| ER | US06 | 10 min. | 8.0 | 48.6 | ||
| ER | Hwy. | 13 min. | 10.1 | 58.7 | ||
| ER | Urban | 6 min. | 2.0 | 60.7 | ||
For the cycle testing, GM is using a two-hour combination of the US urban, highway and the more demanding US06 cycles for the discharge; re-charging for three-hours; and simulating parking for 3 hours. This pattern will run 24x7 for two years on each of the packs. Although the packs are designed to be liquid cooled, the testing on the packs is being done without the cooling. The battery cycling testing is being done at the GM test facilities in Warren and in Mainz-Kastel, Germany.
Although the pack is sized overall at 16 kWh, GM plans to use only 8kWh in operations—i.e., a state of charge depletion window of around 50% (the pack won’t be charged fully to 16 kWh, because with a full pack, the first regen event would begin overcharging the battery). That 8 kWh needs to be deliverable at the end of the battery’s 10-year life, therefore GM is building in a buffer with the 16 kWh pack.
With future iterations of the powertrain, GM may begin expanding the SOC window, and/or begin implementing minor changes in the batteries.
Although the sizing of the pack is conservative, GM’s projected consumption of 200 Wh per mile (8 kWh over 40 miles) is somewhat aggressive. The team is confident in that figure, according to Frank Weber, Global Vehicle Chief Engineer, Chevrolet Volt and E-Flex Systems, because of the testing, modeling and simulation work that they have already done. Nonetheless, the sizing of the pack provides a buffer.
The E-Flex mules that will receive the Li-ion packs for battery testing have already been in operation at the Proving Grounds for 6 months, according to GM, with NiMH packs as the energy storage system. The focus to date with the mules—which implement full E-Flex systems—has been bringing them up to the state of readiness to accept the Li-ion packs and begin dynamic testing. Work on the mules has included:
Software function and integration testing;
Preliminary proof of concept; and
Calibration of the regenerative braking system.
The mules (one of which was on a lift with the Li-ion pack stationed beneath it) have been in operation 6 days a week for two shifts a day. GM expects to have a fleet of Li-ion equipped mules in operation by the summertime.
Over the next six months, GM will be focused on three primary areas with the powertrain: battery state estimation; thermal development; and propulsion development. The latter area includes refinement of the all-electric drive mode, hardware testing in EV mode, and further development of the power electronics.
GM has yet to finalize its selection of the combustion engine component of the powertrain, although the engine will be from its Family 0 of European small-displacement engines (1.0-, 1.2- and 1.4-liter).
GM is opting for a smaller fuel tank than originally conceived to reduce vehicle mass. The tank under consideration will still provide a 400-mile combined range, and GM decided to do as much as possible to ensure its 40-mile all electric range rather than “go overboard” in other areas, such as extended vehicle range. In recognition that the Volt (ideally) will operate for long periods of time without using the engine, GM has modified the fueling system to be able to eliminate evaporative emissions.
Aerodynamics. The inflexible design point of delivering 40 miles all-electric range under a variety of conditions with sprightly performance have forced GM to put a great deal of effort into the refinement of the exterior shape of the Volt. The impact of incremental improvements to the coefficient of drag makes a significant difference at highway speed—much more so than the weight of the vehicle.
The electric range of the Chevrolet Volt is most sensitive to improvements in aero, which is in contrast to a traditional vehicle program in which mass typically plays a larger role.
—Frank Weber
Changes to the shape of the production Volt compared to the show car that GM was prepared to discuss at the briefing included a longer front overhang; more rounded front corners, rather than the sharp corners of the show car; a slightly higher roof; and some modifications to the rear.
GM showed a 1/3 model of the production design of the Volt in the wind tunnel at the company’s aerodynamics lab in Warren, and uncovered small sections (front corner, rear corner) of full-size clay models of the production Volt in the design studio.
The interior. The shape and placement of the battery has pushed the occupants outboard, or to the sides of the vehicle, so the design team worked with the sections of the roof structure and doors to enable aerodynamics and provide adequate head room. The interior will accommodate a 6-foot 2-inch (99th percentile) male comfortably in the front and rear seats.
GM says it is putting a great deal of effort into the development of the human-machine interface for the Volt, although no examples of that were shown during the briefing.
We are looking for an i-Phone like experience.
—Frank Weber
Green Car Congress attended the briefing at GM’s expense.
April 4, 2008 in Electric (Battery), Hybrids, Plug-ins | Permalink | Comments (71) | TrackBack (0)
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Comments
Oh My!.. what is it called when you lust after a car? :)
Posted by: Herm | Apr 4, 2008 12:57:38 PM
... Male.
Posted by: | Apr 4, 2008 1:10:06 PM
That would be car lust. ;)
I for one will stand in line for this car. If GM does the right thing, I think I won't be the only one.
Stephen
Posted by: Stephen Boulet | Apr 4, 2008 1:11:17 PM
need to get this in before the board turns into a gm-bashing contest:
i applaud the engineers at general motors. it is real easy for environmentalists (which i am sometimes) to command engineers (which i am all the time) to "make a better, more efficient product".
how is toyota coming along on their PHEV project? last i heard they were getting disappointing results from their li-ion tests.. i wonder if GM will encounter similar complications.
Posted by: marc | Apr 4, 2008 1:56:53 PM
marc:
EEStor may come to the rescue. With at least twice the energy density and up to 1,000,000 cycles, lithium batteries won't stand much of a chance for year to come.
Posted by: Harvey D | Apr 4, 2008 2:36:50 PM
It sounds like GM are learning a lot from this in terms of energy restricted transport.
Lets hope they apply it to the Volt and to the rest of the range as the models turn over.
If they just applied the aerodynamics to ICE cars, it would make quite a difference.
So good luck to them, and lets hope they succeed.
As Dr. Strangelove says ... "is is only a matter of willpower" ( and money ).
Posted by: mahonj | Apr 4, 2008 2:46:12 PM
This makes me want to believe...
Maybe the term would be autolust, but that just does not sound right :)
Posted by: sjc | Apr 4, 2008 3:40:18 PM
This is fantastic. We are in the midst of an "arms race" for efficiency. Something I've waited my whole life for. Let's hope this long overdue way of thinking makes it to the production line. I am cautiously optimistic...
Posted by: rocknerd | Apr 4, 2008 4:11:03 PM
I doubt GM very much will have this 'Volt' in production by 2010. Since there would already be reports and photos of the pre-production 2010 prototype 'Volt' cars being tested on the roads of America like the 2010 pre-production Camaro.
Posted by: garth | Apr 4, 2008 4:11:20 PM
Do the guys (and possibly gals) who test the batteries really wear lab coats or was that just for show during the tour? I know it's a dumb question but I had to ask after seeing the photo above.
Posted by: rocknerd | Apr 4, 2008 4:16:56 PM
With this kind of movement from GM I don't think my kids will be driving ICEs. Great.
Posted by: marcus | Apr 4, 2008 4:22:45 PM
I think they'll have it production by 2010. They are staking alot of their reputation on this - they are doing tasks in parallel (not the standard process) to get it to production faster.
They should be applauded for their work - and being very public about it. It will be very difficult for them to back away - this has been their poster-child.
Shane
Posted by: shane | Apr 4, 2008 4:32:18 PM
"EEStor may come to the rescue. With at least twice the energy density and up to 1,000,000 cycles, lithium batteries won't stand much of a chance for year to come."
EEstor have made big claims and so far have very little to show for it. despite the fact that big (almost impossible) claims wow the crowds and the journalists, most of the time technological progress is made through small incremental improvements, and all the better for it. don't bet the farm on vaporware, is what I'm saying.
Posted by: eric | Apr 4, 2008 4:36:09 PM
I should add - I have been to technical conferences where this was discussed years ago - some engineers wondered if it was a publicity stunt - but high level DOE officials indicated GM was heavily investing manpower, even at that time. It has only accelerated from then.
If GM beats Toyota to a good plug-in vehicle, it will steal Toyota's thunder. If GM pulls this off, they deserve wide and loud praise.
Posted by: shane | Apr 4, 2008 4:37:54 PM
If the price tag is so high no one can afford it then this is for nothing. It must be priced for the working people at Wal-Mart or the poltry packing plant.
Posted by: Just Watching | Apr 4, 2008 4:57:38 PM
"The interior will accommodate a 6-foot 2-inch (99th percentile) male comfortably"
Well... there goes my dream of owning a Volt in 2010... I'm 6-4. :-(
Posted by: aaron | Apr 4, 2008 6:04:29 PM
I am wondering how much the Volt will weight with 170Kg of battery on top of an ICE engine, a 100KWhrs electric engine plus a generator of 50KWhrs. Probably close to 2 tonnes (4200 pounds) sure GM has a lot to learn how to save weight on the rest of the car to reach a decent mileage otherwise kiss the efficiency.
Posted by: Treehugger | Apr 4, 2008 6:48:26 PM
dont forget there is no transmission.. and they plan to use a small 1.0 liter engine.. so much less than 4000lbs.
Posted by: Herm | Apr 4, 2008 7:24:04 PM
My thoughts on EESTOR:
If what they have is for real they would not signed an exclusive agreement with ZENN, it would have been with GM instead - thinks about it!
Posted by: daverdeam | Apr 4, 2008 7:30:18 PM
"If the price tag is so high no one can afford it then this is for nothing. It must be priced for the working people at Wal-Mart or the poltry packing plant."
Just Watching: Get a job! (or a new one)
There are 100,000's that will buy this car even is it is $40K.
Posted by: daverdeam | Apr 4, 2008 7:34:26 PM
by aaron
"The interior will accommodate a 6-foot 2-inch (99th percentile) male comfortably"
Well... there goes my dream of owning a Volt in 2010... I'm 6-4. :-(
Arrrgh... I also am 6'4" It's just unreal how GM wants to reject a "growing" segment of the population, 6 foot plus people. I'm not asking for much... just a car that I can sit upright in. If GM feels compelled to maintain low hanging ceilings in their cars why can't they design the seat to accomodate 6 foot people??? It's crazy! Design the electric seats to run to the floor, even lower into an indentation in the floor if necessary. Wagoner looks taller than Lutz, can he sit in the car and look out the windshield with his head upright not pressing against the headliner or looking through the blue sun tint band or retracted sun visor? It's just amazing, they want to sell cars and yet, they don't. [sigh] Aaron and I are not the only "tall" people out there. Isn't it interesting that Lutz and Wagoner are tall. Has GM ever reasoned that maybe tall people get noticed and just might have more opportunities for promotion and a higher income than less average height individuals. GM is missing out on $$$$ by not sliding their percentile toward the tall end.
Posted by: itsaboutchoice | Apr 4, 2008 7:38:04 PM
"Do the guys (and possibly gals) who test the batteries really wear lab coats or was that just for show during the tour? I know it's a dumb question but I had to ask after seeing the photo above."
Of course folks in labs wear lab coats. The lab coats and jumpers are part of the Personal Protective Equipment (PPE), just like the safety glasses and safety shoes that they are wearing in the photo. Lab coats protect the wearer and their clothing from dirt, grease, and other nasty things that inhabit laboratories. Lab coats also mitigate the hazard to carrying harmful materials home on worker's clothing. Plus, lab coats can have decals or patches that encourage wearer's to be proud of their work group and their work. Work clothing also reminds the lab workers that their employer may actually give a cr*p about their comfort and safety. (Plus it is usually cheaper to clean a lab coat than replace stained shirts and pants.)
Posted by: mweirick | Apr 4, 2008 7:48:23 PM
"Do the guys (and possibly gals) who test the batteries really wear lab coats or was that just for show during the tour? I know it's a dumb question but I had to ask after seeing the photo above."
Of course folks in labs wear lab coats. The lab coats and jumpers are part of the Personal Protective Equipment (PPE), just like the safety glasses and safety shoes that they are wearing in the photo. Lab coats protect the wearer and their clothing from dirt, grease, and other nasty things that inhabit laboratories. Lab coats also mitigate the hazard to carrying harmful materials home on worker's clothing. Plus, lab coats can have decals or patches that encourage wearer's to be proud of their work group and their work. Work clothing also reminds the lab workers that their employer may actually give a cr*p about their comfort and safety. (Plus it is usually cheaper to clean a lab coat than replace stained shirts and pants.)
Posted by: mweirick | Apr 4, 2008 7:51:14 PM
need to get this in before the board turns into a gm-bashing contest:
So.... Where's the bashing? Is it possible that GCCers are not reflexive GM-haters? That maybe they only bash when the bashing is deserved? That when GM does something good, we applaud them? How 'bout that.
Posted by: George | Apr 4, 2008 9:12:21 PM
aaron,
Not to worry, I am 6'1" and I fit into a Fiero GT back in the day. Hope springs eternal.
Posted by: sjc | Apr 4, 2008 10:32:46 PM
What is the gasoline to wheel efficiency of the gasoline generator to electric motor vs the efficiency of a pure ICE system in creating motion?
I couldn't find any data on the generator used by the Volt excepted it's 53kW and one liter.
Posted by: Laurent GUERBY | Apr 5, 2008 3:59:29 AM
Thanks mweirick. That makes sense. I'm a field geologist so please excuse my ignorance of the indoor side of science.
Posted by: rocknerd | Apr 5, 2008 6:01:34 AM
Can you imagine how many owners are going to "Chip" their Volts to allow increased SOC utilisation from 50% (40 miles) to 90% (72 miles EV range) if it turns out the batteries can handle some more!
Posted by: clett | Apr 5, 2008 6:19:12 AM
@ Laurent Gerby -
given the large size of the battery pack, it will be possible to operate the naturally aspirated ICE either at its point of minimum specific fuel consumption or not at all. For an engine rated at 53kW, that translates to 35-40kW shaft power.
Given this small size, the block should heat up quickly but after that, heat loss to the coolant may be greater than usual (especially for per-cylinder displacements below 400cc). Figure ~30% efficiency for the ICE because of that optimal operating point. This compares to ~20% for average efficiency for the engine in a conventional drivetrain subjected to a mild drive cycle (i.e. not US06).
However, the shaft work produced by the little engine that could has to be turned to AC electricity, rectified to DC, possibly buffered in the battery pack, then inverted to AC of a different frequency and/or frequency and then converted back into shaft work to drive the wheels. This series hybrid transmission is quite inefficient, figure ~70%, and compares to ~96% for a mechanical transmission and differential (torque converter locked up).
Ergo, series hybrid: 0.3*0.7 = 0.21, conventional 0.2*0.96 = 0.19. If these rough numbers hold, the series hybrid should deliver around 10% better fuel economy on gasoline once the ICE gets fired up and the battery goes into charge-sustaining mode.
However, note that GM will use an off-the-shelf automotive ICE in the first iteration to reduce development risk. Prime movers that are optimized to run in a narrow speed and torque range may follow later and yield further improvements in core efficiency as well as other relevant parameters, e.g. criteria emissions and NVH. Moreover, there will be further improvements in electric motor/generator, power converter and battery charge/discharge efficiency.
The bigger issue will be bringing down cost.
Posted by: Rafael Seidl | Apr 5, 2008 6:39:19 AM
Laurent: last I read, they hadn't fixed on the actual generator they will use.
Daverdeam: re EEStor, the exclusivity of ZENN is only for cars under a weight limit (less than standard family sedan). From one article I read, Denise Richards saw the specs on the EEStor and decided against using it (I'm not sure what factor she didn't like)
Posted by: Neil | Apr 5, 2008 6:39:27 AM
@Rafael,
Remember the critical advantage of the series-hybrid powertrain is the complete lack of design restraints relating to engine throttle response, driveability, smooth torque curve, idle quality etc.
An engine for generator use only is "freed" from the inherent constraints of the Otto cycle and can be designed with very different architecture for very high thermal efficiency.
For example, an aggressive downsizing using 15:1 expansion ratio Atkinson cycle and very high boost levels with otherwise unworkably long spool-up time is readily accommodated with a series-hybrid drivetrain, so any additional losses from generator to wheel can be more than made back in better engine efficiency.
I think thermal efficiency of the engine alone could reach 45%+ in this type of setup, more with CI, and that will knock the conventional powertrain into a cocked hat.
Posted by: clett | Apr 5, 2008 7:20:28 AM
Laurent asked about gasoline to wheel efficiency. When we were doing presentations on PHEV's to Washington state legislators a year and a half ago, the GM presenter stated that they expected to get 50 miles per gallon when the Volt was running on gasoline. I think that is overly optimistic but if it comes close, I believe we'll be seeing a lot more series hybrids in the future. They are really just all-electric vehicles with a range extending generator on board.
Posted by: James White | Apr 5, 2008 8:01:17 AM
Re: ESStor ESSU:
The highway capable Zenn will supposedly use a very quick charge (5 minutes) Esstor 50 KWh ESSU to get 400 Km between charges in late 2009.
If this comes true, and more people believe that it will, pure ICE cars, Hybrids and even PHEVs may have to be progressively phased out in favour of EVs.
Alternatively, Hybrids and PHEVs could use Esstor's ESSUs to reduce weight and recharge time, to get many more cycles (extended operation life) and get more electricity driven distances.
The ESStor ESSU (with its 1 million potential cycles) seems to be the ideal unit for V2G & B2G and for Solar and Wind power installations.
It may all sound too good to be true but I hope that enough can be produced to satify the huge demand, especially if the mass production price is below $250/KWh.
Posted by: Harvey D | Apr 5, 2008 8:07:54 AM
Rafael
And bringing the weight down! like you point out the overall efficiency of a series hybrid is not that great but you have to add the extra weight inherent to this type of architecture that will also diminish the mileage.
So in the end I think Toyota should achieve better overwhole efficiency with a parallel hybrid plug-in architecture.
Posted by: | Apr 5, 2008 9:19:12 AM
Rafael
I think your figure of 96% efficiency for a mechanical transmission is overly optimistic, the efficiency of a mechanical transmission from engine to wheel is more like 85%, isn't it ?
Posted by: Treehugger | Apr 5, 2008 9:22:59 AM
Clett
45% sounds more like a diesel, an Otto Atkinson peak at 37% in the very best case.
Posted by: Treehugger | Apr 5, 2008 9:25:46 AM
I read something about the series hybrid concept being in the public domain domain for quite some time, so there are less patent problems. That might have just been some author's speculation, but if patents are keeping products off the market that would benefit us all, they are not helping.
Posted by: sjc | Apr 5, 2008 10:19:12 AM
The prior-gen Prius engine benched at 37% peak efficiency and achieved 33% or greater over most of its relatively narrow operating range. With an even narrower range, GM should be able to average 35%. Serial drivetrain efficiency of 70% is very pessimistic. The Volt ICE should run close to road load, so most electricity gets sent straight to the drive motor instead of being converted to DC and stored in the battery. Such a scenario should deliver 85-90% efficiency. This compares well with the Prius drivetrain, which combines mechanical and electrical power paths.
With Prius-like engine efficiency and Prius--like drivetrain efficiency the Volt should achieve Prius-like extended range operation of about 45 mpg. That's pretty close to the 50 mpg originally mentioned by GM.
I am wondering how much the Volt will weight with 170Kg of battery on top of an ICE engine, a 100KWhrs electric engine plus a generator of 50KWhrs. Probably close to 2 tonnes (4200 pounds)
As mentioned by others, using a 1.0L 3 cyl ICE and eliminating the transmission will save around 200 kg. The gas tank will be 8 gal smaller than typical, saving another 25 kg. The battery case is a structural element, saving a tad more. The Volt will be heavier than a similar ICE-only car, but not that much. Also note that weight does not harm mileage as much for a car with regen as it does for an ICE-only car.
Posted by: doggydogworld | Apr 5, 2008 1:47:59 PM
Keep in mind, the Toyota Prius is both a parallel and series Hybrid.
At low speeds and high acceleration, the IC engine of the Prius mostly drives a generator which then drives the electric motor.
Posted by: globi | Apr 5, 2008 2:03:49 PM
"That will proceed in parallel with the pack-level tests in the battery lab that will continue for almost two more years—the shortest amount of time into which GM could compress testing to validate the required 10-year, 150,000-mile lifespan of the packs."
This seems to be the big issue as to why GM is looking at 2010 for a release date. Who made the 10 year rule?
Why does GM (or any other mfg like Ford,Toy,Honda) need proof of a 10 year battery life? Sell the Volt this year with a disclamer. Maybe the battery will only last a year or two. When Bill Gates created Windows he
didn't perfect the software before selling it. Was that a bad move on his part?
I have always had a soft spot for the Chevy. Something
about the car...I just can't explain. If you know then you know. I want GM to step up with the EV. GM is AMERICA! If we have to wait until 2010, I'm afraid this oil addiction is going to take us under.
Posted by: Jerry | Apr 5, 2008 2:44:34 PM
10 years out of a rechargeable lithium battery pack is a long time.. A123 claims they can do it so lets hope for the best. Old style wet nicads from the 60s were famous for lasting decades.. last time I bought one was in 1985, suplus NASA from the 60s.
Posted by: Herm | Apr 5, 2008 3:33:51 PM
I'm sure GM will make that chip impregnable
Posted by: Herm | Apr 5, 2008 3:35:40 PM
It seems like GM is protecting their brand. Ford could have brought out the Escape hybrid 1 year earlier for customer testing, but chose to test in house for another year. November 2010 will be here before you know it. If the oil situation is so bad that we can not wait until then, bringing it out sooner would not have helped anyway.
Posted by: sjc | Apr 5, 2008 3:52:40 PM
Dogydog...
Thanks for the details, that sounds convincing. GM still has to prove that they can introduce seamlessly such a new architecture just as Toyota and Honda did it for the hybrid
Posted by: treehugger | Apr 5, 2008 7:02:34 PM
Hi Treehugger, re Rafs 96% Tx loss, you beat me to it. But I have seen losses of 98% quoted in some places for manual transmissions. LOL
As a matter of fact even plain spur gears 1:1 are 95%. For 1:3 ratios factor in about 93%. All vehicles do a double reduction at least and the one between the driveshaft and layshaft has got to be 90% at low load what with up to 6 pairs of meshed gears churning the oil. I figure 81% for FWD and you can figure another 70% for the hypoid reducer in a RWD which is why Chrysler is abandonning a new RWD platform - for fuel effcy reasons.
A pure series hybrid with something approaching 95% conversion each at both generator and motor is streets ahead which is one reason I favor them. Hey, even the '04 Prius is not exempt with a whopping estimated 81% for its triple reduction following the PSD gear system. (Source DOE reverse engineer/competitive benchmarking 2004) And with its concentric driveshafts I can't even begin to calculate the average torque loss of the PSD itself.
T2
Posted by: T2 | Apr 5, 2008 11:33:53 PM
Many thanks to all who provided information on efficiency. It looks like efficiency using generator is higher than ICE, so now I wonder why everyone is talking about batteries. We could produce generator based vehicles right now and get better batteries over time, no?
Posted by: Laurent GUERBY | Apr 6, 2008 1:44:48 AM
@ clett, treehugger -
there is significant room for improvement in efficiency, but bear in mind that small, high-speed reciprocating engines are inherently less efficient than large ones. Core efficiencies in excess of 40% would be an extremely tall order for small spark ignition engines, I'm sure there's lower hanging fruit in the electrical transmission.
As for vehicle weight, it's an issue but less so - at least in city driving - if you have efficient recuperative braking. There's still lots of room for improvement there, too.
@ treehugger, T2 -
a modern set of spur gear will transmit 97-99% of shaft power (depending on gear ratio). In a typical manual transmission, there are three sets of spur gears between crankshaft and wheels, so 96% probably isn't far wrong.
The poor transmission efficiency referred to by treehugger is roughly correct for old automatic transmissions that don't feature a lock-up clutch for their torque converter. In Europe at least, there is no market for such gas guzzling designs. For example, Mercedes engages the lock-up clutch even in first gear, so the torque converter is only active when accelerating from standstill and, during gear changes.
Posted by: Rafael Seidl | Apr 6, 2008 5:04:49 AM
Laurent,
The batteries are there for what has been referred to as "load leveling". I first saw this term used in the PNGV program. It means that the engine can run at highest efficiency when there is some storage to supply the power surges needed for acceleration.
Posted by: sjc | Apr 6, 2008 9:27:41 AM
It all sounds just a little too cozy. GM is the great Satan, G Bush is the parent and the two working together may be trying to kill the EV industry with a Volt failure. Do not underestimate the backdoor intent of US automakers, Bush against the world pols, and oil industry capitalists angling to kill the EV a second time. Why not make public transit free and phase out private cars entirely?
Posted by: doubtful | Apr 6, 2008 12:10:12 PM
@doubtful
Could this be it? The long-awaited GM bash? Or is it a Bush-Bash? Hard to say.
Posted by: George | Apr 6, 2008 9:30:01 PM
Fantastic! They can't produce this soon enough!
Posted by: Robert Martson | Apr 6, 2008 10:08:21 PM
@ Treehugger,
"45% sounds more like a diesel, an Otto Atkinson peak at 37% in the very best case."
The Prius "Atkinson" cycle engine still has many design constraints that prevent it from reaching higher thermal efficiency. Contrary to popular belief, Prius was designed to minimise exhaust pollutants rather than maximise mpg.
Such limitations include the fact that it still has a physical connection to the road, has a requirement of quick spooling up to meet power demands, and only has a 13.5:1 expansion ratio. Without these constraints, it could easily have forced induction with compounding to recover exhaust gas heat energy and 17:1 expansion ratio. A "BMW steamer" type affair would also work well with a genset arrangement to further boost efficiency. The ICE is far from reaching its thermal peak.
Posted by: clett | Apr 7, 2008 3:26:15 AM
My compliments to the posters above for keeping this (mostly) a bash-free zone. Refreshing!
Posted by: Schmeltz | Apr 7, 2008 6:12:57 AM
@ Raf - You wrote " a modern set of spur gears capable of 97%-99% dependent on ratio" or words to that effect. Well I'm still rebutting your claim. The following evidence is not the best source I've seen to support my contention that 93% to 95% is more likely but it is a step in that direction, with real world testing.
http://www.ornl.gov/~webworks/cppr/y2001/rpt/121813.pdf
Fig 2.5 [18 of 43] and Pg 31 [39 of 43] are especially relevant.
Try the same link with 122586.pdf for more competitive benchmarking of the Prius drivetrain.
I became sensitized to some ( yet to be substantiated ) quotes in spur gear efficiency when I perused a collection of research papers put together for the EVS-7 (Electric Vehicle Symposium) back in 1983. One DOE project overseen by Eaton Corporation had a section devoted to load tests of their twin ratio gearbox with its hydraulic shifter.
This formed part of a high speed induction motor transaxle and would probably be a two stage unit.
They found an overall loss of 95% for 1:1 and 93% for the 1:3 if memory serves me.
There is another pdf from a winter workshop a couple of years back which I will post later regarding a series of block diagrams of the power transfers between different parts of the Prius powertrain at different types of loading - accelerating, cruise, coasting and braking etc. These diags held a lot of data but studying it intently I happened to notice that the author estimated a neta of 18% for the Prius transaxle following the PSD. So there are others out there whose life experiences would seem to support my point of view.
T2
Posted by: T2 | Apr 7, 2008 7:06:38 AM
Erratum My previous post should have read neta equal to 82% of course.
@ Raf
First I must admit I do agree with your following statement :
"However, the shaft work produced by the little engine that could has to be turned to AC electricity, rectified to DC, possibly buffered in the battery pack, then inverted to AC of a different frequency and/or frequency and then converted back into shaft work to drive the wheels. This series hybrid transmission is quite inefficient, figure ~70%, and compares to ~96% for a mechanical transmission and differential (torque converter locked up)."
Even if I feel that mechanical 96% figure is way too generous, churning power in and out through the battery is really inefficient as you point out. A spokesman for GM said they wouldn't be doing this in common practice. Much of the generated energy would find its way directly to the traction inverter only the spillover would find its way to the battery, but whatever. I feel leaving the energy in the gasoline until you need to use it is overall more efficient. Using the plugin derived energy for peak loads sounds way better idea than depleting to zero and only then firing up the genset. But that's just me. I am not in favor of PHEVs anyway - unless someone out there is figuring to start WWIII.
Raf, I want to pick up on a later post where you say
"there is significant room for improvement in efficiency, but bear in mind that small, high-speed reciprocating engines are inherently less efficient than large ones."
In my opinion efficiency in itself, is not that important compared to low mass. However the operating strategy should be to run any size of engine as close to its maximum torque as practicable so that the resulting much lower rpms needed will minimise frictional losses. Toyota has maintained that being its strategy for the Prius system from the very beginning of which I am sure you are aware.
That said, conventional operating strategies are completely the converse. What we have today are comparitively large engines running lightly loaded even in 5th gear. With the fixed gears of stepped transmissions this is necessary to allow for convenient acceleration at any instance without the immediate need to change gear. The equivalent effect with a series hybrid, whose engine is always fully loaded, is to rapidly spin up to those higher rpms where it can generate the required extra power and be able to do this before the vehicle itself has even begun to accelerate. Calling on high rpms to do this are only inefficient if torque demand is low but in a series hybrid the traction inverter would be able to provide exactly the right electrical load on the generator to maintain the maximum torque demand on the engine. Consequently the generator should always be operating from the most efficient parts of the engine map.
T2
Posted by: T2 | Apr 7, 2008 12:45:45 PM
Judging by the comments, the US driving public has Great Expectations for this WunderWagen. And why should they not? They have been waiting for something like this for decades.
However, I fear you are going to be let down again. Only 8kWh real capacity - so 30 miles AER, let's be realistic. More importantly, how many of these cars will there be? 10,000 pa? 20,000 pa? 50,000 pa? The waiting list will be from here to the Moon.
Unfortunately, this will be a vehicle for the elite who will pay $35,000 - $40,000 for a 2 seater or 2+children.
This is not going to be the Volk's Wagen.
Posted by: Emphyrio | Apr 7, 2008 12:48:30 PM
Okay, I tried to be nice but that didn't work. Here comes the bash! I did not get any answers to my question: Why does GM hold the production of the Volt until they confirm that the battery will last 10 years?
Who has ever heard of a battery lasting 10 years? Who is expecting the Volt battery to last that long? (besides GM) This sounds like an excuse to test for at least two more years before releasing the Volt. If asking this question makes me a GM bashing sheep then all I can say is Baaaaaaaaaaa
Posted by: Jerry | Apr 7, 2008 6:52:40 PM
Jerry Gm has a 10 year 150l mile warrabty and NOTHING will lower that.
By not slacking on warrabty they sebd a message that yes THIS electric car will be dependable and will last you even if times get hard and you have to hold on to it a long time.
Posted by: wintermane | Apr 7, 2008 7:29:46 PM
They may be going on other battery warranties for hybrids. If I were bringing out a series hybrid and I were a large car company, I would want everything to go right. If our company brings out a product that has a major flaw, it could be the end of us. We would lose whatever credibility that we have left and all our product lines could suffer.
Look at upside versus downside. If they are late brining out the product, they say that they want to get it right and will lose a bit of revenue. If they rush it and get it wrong, they could lose the whole ball game. I am not a major fan of GM's executive staff nor their so called decision making process, but in this case I can understand it.
Posted by: sjc | Apr 7, 2008 8:54:59 PM
@T2, "churning power in and out through the battery is really inefficient"
This was certainly the case for old-skool chemistries like lead-acid, or NiMH, which give out only 65-75% of the energy you originally put in due to internal losses.
However the newer lithium-ion chemistries with very low internal resistance can reach 98-99% in/out efficiency. This development is another enabler of the series-hybrid drivetrain.
Posted by: clett | Apr 8, 2008 1:32:24 AM
Jerry, all hybrid batteries are guaranteed for 10 years. GM knows the Volt will not sell if customers have to replace a $10k battery every few years, just as the Malibu would not sell if you had to buy a new engine and transmission every 3-5 years.
Posted by: doggydogworld | Apr 8, 2008 9:29:24 AM
doubtful: Making public transit gratis is a seemingly noble idea which has been demonstrated to be extremely flawed for most locales, especially in the US:
National Center for Transportation Research:
ADVANTAGES AND DISADVANTAGES OF FARE-FREE TRANSIT POLICY
Posted by: Santos | Apr 8, 2008 8:06:45 PM
The problem with the 10 year warranty is that is what drives the requirement to only drain the battery halfway, to treat it gently.. otherwise you could use a pack half the size and weight and get the same all electric range. I guess as the years pass and the tech improves this will change. Perhaps the cells will get so cheap that we can afford to replace them every 3-5 years.
I know for a fact that A123 lipos are way tougher and longer lived than NIMH cells such as the ones used in the Prius.. so perhaps they are being too conservative.
Posted by: Herm | Apr 9, 2008 3:44:52 AM
@Clett,
You're saying the higher power density of Li-ion would have to translate into corresponding lower internal resistance which should raise "churning" efficiency. I'll buy that.
T2
Posted by: T2 | Apr 9, 2008 5:49:48 AM
About the 10 year battery life. First of all, they're clearly not ready to shove these cars out the door; battery packs or not. It took Toyota 3 years to develop and sell the Prius in a very accelerated engineering program and that did not include however long it took Toyota to convince themselves to even try to do it. The Volt debut as a concept car was in 2007, so GM had not even convinced themselves to do it and here they are slating for 2010. That's about as aggressive as the Prius development (maybe more, maybe less, depending on how you want to look at it, but it's in the ballpark).
I do expect the batteries to last 10 years.
Disposable cars or batteries is not very green and these batteries are not cheap, either.
But beyond all that, GM really needs to make a quality car with this. Don't take that as GM bashing (well, maybe) but there's a lot more reputation than GM's riding on this vehicle. Good or bad, the EV1 set the perception of BEVs for a decade and this car has the potential to do the same for ER-BEV. So, I think their schedule is probably about right. Much faster and the car will be half baked, much slower and they will miss the opportunity.
Posted by: DaveP | Apr 10, 2008 5:26:14 PM
Wasn't GM involved in killing the electric car? I don't feel comfortable supporting a company jumping on the green bandwagon because gov't regulations is forcing this change on them. There are electric car companies with positive intentions such as Zap that are focusing on the publics demand for cleaner cars. Check out this company. www.zapworld.com
Posted by: Bill | Apr 15, 2008 11:35:31 AM
Bill,
$11/barrel oil in 1998 killed the electric car. But $110/barrrel oil plus improved battery technology has paved the way for a transformation of the auto industry. Most people, myself included, would prefer to buy a car from Toyota, Honda, or yes, even GM, than from a small startup. I wish Zap and others all the good fortune in the world, but I want a mass-produced, mass-marketed automobile. That's why I bought a Prius, and hope to one day buy a GM Volt.
Posted by: JamesEE | Apr 20, 2008 9:51:08 AM
Battery life:
If you don't make a quality car (which means a reliable one plus many other attributes), then you will lose marketshare or eventually go out of business. All the domestics have been radically improving their product quality over time having learned this lesson. For people to claim that this isn't an important factor is some very weak arm-chair commentary. It's not a formula for success and all suggestions that they compromise the 10year/150,000 should simply cease. These may be "batteries" but they are fundamental (and very expensive) key powertrain components... not 3-4 year replacement components that you can buy at Wal-Mart.
Plus, anyone who really wants the PHEV/eREV concept to succeed, should NOT encourage any strategy which may give the early products bad reputations which might then taint the entire concept and hamper its adoption.
Posted by: davet | Apr 20, 2008 10:40:57 AM
Efficiency discussion:
I strongly agree with the comment that there is upside improvement on the overall efficiency..but I believe it is much more than 10% (over time). This is the first real production generation of an eREV/series hybrid. Not only will there be a lot to learn and improve (a natural evolution of product engineering) but there are new technologies that are enabled by a series eFlex system.
For example, I think the series hybrid configuration may finally make HCCI (Homogeneous Charge Compression Ignition) viable for high volume production automobiles. The challenge with HCCI has been control across the load & RPM range. So wouldn't a Volt-eFlex-HCCI platform better enable the ICE range extender to operate in a narrow RPM and load region which would greatly simplify the control challenge? So the decoupling of the ICE engine from the driven wheels, perhaps combined with new in cylinder pressure monitors, finally may enable the first volume production HCCI engine (for any car).
Think of how much progress has been made on conventional ICE driven autos over 100years.. we've never had mass market viable EVs which have driven the virtuous cycle of investment->innovation->improvements+cost reductions->further investment. So, I think 10% is a somewhat pessimistic estimate of the improvement possible if we get PHEVs/eREVs to the point of being mass market viable.
Posted by: DaveT | Apr 20, 2008 10:59:11 AM
To Discussion of "Not being a People's car" if the cost is $35k+
Folks, advanced technology costs money.. both fixed investment in technology and product development AND variable costs of manufacturing. Many times a new technology has to start from the high end of a product line and then trickle down to the broad market. Think of airbags, abs, AirConditioning, AutoTransmissions or for electronics in cell phones, big flat panel TVs.
As long as there is sufficient volume at the higher initial price (and a belief in the market potential of the technology) to then encourage investment in subsequently higher volume products, follow-on cost reduced designs, investments to drive higher manufacturing yields, and other moves to amortize the fixed development costs and to reduce the variable manufacturing costs, then over time the extra costs will decline and the technology can be deployed in progressively more products.
Posted by: DaveT | Apr 20, 2008 11:12:20 AM
gggggggg
Posted by: | May 22, 2008 12:56:14 PM
