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.

Thanks mweirick. That makes sense. I'm a field geologist so please excuse my ignorance of the indoor side of science.

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!

@ 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.

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)

@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.

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.

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.

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.

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 ?

Clett

45% sounds more like a diesel, an Otto Atkinson peak at 37% in the very best case.

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.

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.

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.

"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.

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.

I'm sure GM will make that chip impregnable

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.

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

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

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?

@ 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.

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.

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?

@doubtful

Could this be it? The long-awaited GM bash? Or is it a Bush-Bash? Hard to say.