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Determining the Appropriate Design and Configuration of PHEVs

A set of papers presented yesterday by engineers from Toyota, Argonne National Laboratory and GM at the SAE 2008 World Congress explored the impacts and requirements of different types of plug-in hybrid electric vehicles (PHEVs)—specifically extended range electric vehicles versus a blended power split approach.

The Toyota paper, Study on the Potential Benefits of Plug-in Hybrid Systems, started by noting that while plug-in hybrids can address the three big issues facing transportation—fuel consumption and energy diversification; greenhouse has reduction; and air quality—breakthroughs in battery energy density, reliability and cost must occur.

Toyota’s basic argument is that the costs and trade-offs of deploying an extended range electric vehicle architecture at this time outweigh the benefits, and that blended systems have greater benefit at this point in time.

Toyota considered a series hybrid with a small ICE as a range extender using an EV strategy (e.g., the Chevrolet Volt) and a parallel hybrid with a plug-in pack using a blended strategy (e.g., the Toyota PHV based on the Prius).

Using the US06 cycle to represent typical North American driving, Toyota concluded that up to 100 kW of output is required to drive that cycle in a mid-sized vehicle. The company then considered the operation of a blended system designed for charge depleting operation over the city cycle. Toyota concluded that maximum output required is approximately 40 kW, and the average was less than 20 kW.

An analysis of the impact of reducing battery power showed that while a 40 kW battery enabled all electric operation almost 100% of the time in the city cycle, using a 20 kW battery still enabled electric operation 95% of the time. An extended range vehicle, Toyota pointed out, would require a battery, motor and electrical system capable of providing maximum power (100 kW).

Toyota also concluded that while CO2 reduction increases for PHEVs with longer all-electric range, the benefit is not linear, and that as EV range increases, CO2 reduction levels off due to the high percentage of drivers with short daily driving distances.

Toyota argued that providing increased EV range increases vehicle cost due to higher battery cost; reduces luggage space; and increases fuel consumption in charge sustaining mode due to increased battery mass.

A paper from Argonne National Laboratory, Comparison of Powertrain Configuration for Plug-in HEVs from a Fuel Economy Perspective, analyzed several PHEV powertrain configurations, including series (e.g., Volt), pre-transmission parallel (e.g., the Sprinter van) and power split (e.g., Prius) with respect to component sizes and fuel economy for 10- and 40-mile all electric range (AER) applications.

Argonne sized the batteries in its evaluation (which used the Powertrain Systems Analysis Toolkit, PSAT) to follow the UDDS urban cycle while in all-electric mode, and to meet the AER targets for the vehicle. Argonne also specified that the PHEV would operate in electric-only mode at higher vehicle speed in comparison with regular hybrids.

Component Sizes in Argonne Study
Parameter 10-mi AER 40-mi AER
Pre-trans Par. Split SeriesPre-trans Par. Split Series
Engine power (kW) 76 74 109 79 77 114
Propulsion motor (kW) 48 62 90 50 71 95
Generator power (kW) NA 63 106 NA 65 111
Battery power (kW) 58 52 55 61 64 58
Battery capacity (A·h) 18 21 18 71 69 71
Total vehicle mass (kg) 1,675 1,667 1,700 1,764 1,800 1,794
Simulated fuel economy results under urban and highway test cycles for the Argonne study of three different configurations in 10AER and 40AER cases. Click to enlarge.

In terms of fuel economy, Argonne found that the split configuration provided the best fuel economy. The series configuration suffered from dual power conversion—from mechanical (engine) to electrical (generator) and back to mechanical (electrical machine). Engine efficiency was higher for the series configuration that for other configurations, and electrical efficiency was practically identical for all three configurations.

The Argonne researchers concluded that:

Although both the power split and series configurations require two electric machines and an engine, the series configuration, as expected, requires significantly higher component power as a result of the many component efficiencies between the engine and the wheel.

In terms of efficiency, all of the configurations achieve similar characteristics when operated in electric mode. Both series and power split configurations do not use a multi-gear transmission, but the parallel configuration makes up for losses by operating the electric machine at higher efficiency points. In CD mode, the power split provides the best fuel economy as a result of its dual path of power form the engine to the wheel.

On the basis of the thermal and electrical consumption analysis, series configurations appear to be an appropriate choice for vehicles designed to provide long AER because of their simplicity in terms of control and their ability to operate in electric-only mode at high vehicle speed. The power-split configurations appear to be a valid choice for vehicles based on a CD approach.

The GM paper, The Electrification of the Automobile: From Conventional Hybrid, to Plug-in Hybrids, to Extended Range Electric Vehicles, was presented in an earlier form at the 2008 SAE Hybrid Vehicle Technology Symposium in San Diego (13-14 February). (Earlier post.)

GM is currently developing both a blended strategy PHEV (the Saturn VUE Green Line PHEV is a derivative of the conventional 2-Mode Hybrid) and the extended range electric vehicle (E-REV), the Volt.

For the paper, GM simulated the performance of a mid-size sedan with a conventional powertrain; an HEV with a 40 kW electrical power constraint; a converted PHEV with a 35 mph (56.32 kph) speed constraint, a 40 kW electrical power constraint, 3.5 kWh of usable electrical energy (as opposed to total battery pack energy), and a blended operating strategy; an urban-capable PHEV with a 60 mph (96.56 kph) speed constraint, a 53 kW electrical power constraint, and 3.5 kWh of useable electrical energy; and an E-REV with 8 kWh of useable electrical energy and EV capability not limited by electric power or driving speed.

The key to the results of the simulation is the use of the operational data from 621 drivers captured in the Southern California Association of Governments (SCAG) Regional Travel Survey (RTS).

Net battery energy versus distance driven, compared to the requirements of the three different cycles. Click to enlarge.

GM calculated the driving intensity—the net energy per mile (kWh/mile)—required by the urban cycle, the highway cycle, and the much more aggressive US06 cycle, then compared these to the RTS data. (See diagram at right.) They found that while only 3% of the real-world drivers fit within the urban cycle and 21% fit within the highway cycle, fully 97% fit within the requirements of the US06 cycle.

GM concluded that:

  • The real-world RTS data set contains widespread and significant driving at power levels and speeds beyond that represented by the urban driving schedule.

  • An E-REV is more than ten times as likely to finish the day as an EV than as urban-capable PHEV derived from an HEV, when operated in the actual application, as represented by the RTS data set.

  • An E-REV will consumer, on average, less than half of the petroleum of a PHEV in the real world, if overnight charging is assumed.

  • An E-REV will reduce regulated emissions that are due to initial trip starts by more than 70% when compared to a PHEV in the actual application

  • Electric range when operating on the urban schedule is not a direct measure of a plug-in vehicle’s ability to run with the engine off, ability to displace petroleum or ability to reduce regulated emissions in the actual application. Rather, the ability to run with full performance on electric power alone leads to improvements which would be realized in actual application.

  • In the event of a petroleum disruption, an E-REV could support uncompromised vehicle operation for the majority of drivers.

We conclude that electrification that enables E-REVs may be well worth the effort. Specifically designed electric powertrains, incorporating higher power motors and thermal systems, higher energy batteries and integrating them into vehicle structures specifically designed for that purpose will be rewarded with societal benefits in real world use. While PHEVs can make improvements compared to HEVs, an E-REV appears to realize a much greater portion of societal benefits.




Toyota : RAV4EV never existed. It was a mirage. the happy owners are all lying


Kert: Hee, hee, hee.

Given that Cobasys is on the ropes now, I don't see why someone shouldn't start punching out EV-95 type batteries.

Also, hint to Toyota: high, but short power requirement (US06) equals ultracap.


"..40 kW battery enabled all electric operation almost 100% of the time in the city cycle, using a 20 kW battery still enabled electric operation 95% of the time."

I contend that the Volt could have 20 mile EV range and still be useful and sell. We have to start questioning some assumptions and actually talk with millions of people that would use the product, before we make huge committments.

Hybrid fan

"the costs and trade-offs of deploying an extended range electric vehicle architecture at this time outweigh the benefits, and that blended systems have greater benefit at this point in time."

That's the bottom line. For all the idealistic appeal of electric vehicles, they are far too battery intensive. Especially given today's supply situation with today's batteries. In order to build 1 all electric, you'd need the batteries from 4, 5, even 10 gas/electric hybrids.

Both from an environmental and a business model point of view, all-electric just doesn't make sense today. Maybe someday. Hopefully, someday soon. But not today.

Harvey D

It seems that all parties are doing their best to sell their own design. There is nothing wrong with design diversity as long as it is not used to delay the arrival of better Hybrids, PHEVs and BEVs.

Toyota seems committed to improved Hybrids for the short term (3 to 5 years) and PHEV/BEV after 2012/14 or whenever their own Li-On pack is ready. GM may have to curtail or postpone mass production of the Volt PHEV until batteries are improved and their price come down (2012/14?). GM may produce a few thousands Volts in 2011/12/13, at a loss and/or to satify the hard core and polish their image.

All (rightfully?) claim that battery pack weight, size and cost are the main restrictions to the production of affordable PHEVs and BEVs.

Unfortunately, with the possible exception of the ESStor ESSU and Combo supercaps-batteries, there are no major breakthroughs on the horizon. Without much stronger interventions,
battery pack evolution may follow the standard (8%/yr) improvement curve. At that rate, it will take 7 to 10 years to mass produce suitable batteries for affordable PHEVs and BEVs.

For now, and the next 3 to 4 years, the best buy is a Toyota Prius, and even more so, the new generation improved Prius in January 2009. For those of us who prefer a larger car, the Camry Hybrid new generation will come out a few months latter.


Using the US06 cycle to represent typical North American driving, Toyota concluded that up to 100 kW of output is required to drive that cycle in a mid-sized vehicle.

100 kW for a mid sized vehicle? What kind of test is that? Does that include a 0-100 kph in less than 8 seconds or what? The current Prius is no snail, but it has a peak power of 'only' 85 kW, meaning it could not successfully complete the test. As would many other midsized cars. Can anybody enlighten me on this?


Hybrid fan: Battery use in cars is not a zero sum situation. If GM wants to build the Volt, then the battery supplier is likely to build a new factory to build more batteries.

Fabio Ferrai

Anne, usually drivers call “snail” cars with less that 50W per kg...
I’m not an expert of the US driving cycle, but I can tell you that the European cycle was design to be passed by snail cars… These cycles are far from reality, but it is a standard.


i read an article today that the reason batteries are soo expensive is because of the chemistry and location to get the lithium from the ground. in the past couple of years, they have found a deposit that mother earth has dried up and done most of the processing already. they are now building facilities to hardvest this material. thus the couple of year turn around for supply is due in large fact to this new set of deposits found that will bring lithium costs way down. it was stated that the amount of lithium in these deposits are as vast as those of oil found in saudi arabia. thus our battery needs are close to being fulfilled at a price point that is acceptable.

so yes, "today" the prius system is the better choice. but in two years, the volt is the better choice. in two years, the lithium will be flowing from those deposits and into our cars at a price point we can all afford.

an ev is desired for most daily drivers under 40 miles. the volts is perfect and hits the points on the head in many areas. the big one for me is daily life continues no matter what is going on in the rest of the world. wars happen...always. a disruption in oil will make prices go _way_ higher for everything in our lifes. an e-rev that works under my daily commute on all electric is just smart and economically the best choice.

i'm just glad we all get what we want (e-rev, phev, etc.). at least we all have a choice and competition only makes all of these products better.

chevy volt e-rev or zap alias e-rev
whichever one comes in first and under $35K. the volt prob won't be under $35k and the alias prob wont make the timeline.

Andy Frank

All the comments make sense relative to each configuration, But GM has introduced another term that is perhaps confusing the issue. They define a PHEV and an E-REV as diferent animals.

They are essentially the same from a pure electric range point of view. they do this to differentiate between their 2mode Plug In and the Volt Series Plug In.I think this is unnecessary since either it is a plug-In or it is not!!

All researchers are missing the use of a high efficiency CVT which none of them has!! This changes their conclusions.

Prof Frank


actually splitting up the e-rev and phev is just. i plan on using my e-rev for under 40 miles per day. this means that i will not be using gas at all. thus i imagine filling up my five gallon tank maybe every other month with weekends being over 40 miles. with a phev pruis, i couldn't do that. i would still need to fill up the small tank on some regularity. all-electric mode is why e-rev. if you never go over that with your daily car, the vehicle is a non gas user.


Let the market decide - if you can't buy it, it may as well be vapour.
All that matters is the MPG and CO2 levels (and cost) on a weekly or annual basis.
Once you have some actual cars, you can see what works.
Right now, it is hybrid for urban, diesel for the open road.
Both are going in the right direction.

I guess the trick with hybrids is to figure out how to get the most out of each extra KWh of battery energy, and how to recover as much braking energy as possible.

Fabio Ferrari

Yes Frank! I can tell you that French car makers are very septic about HEV… but really embarrassed when you speak transmission and refer to the Toyota eCVT system! Even if they finally say that a good diesel with a dual clutch is "better"…


Andy: Could you please expand on your use of CVTs in the cars you've built and how that affects these calculations?

P.S. at one time even GM was referring to the Volt as a series hybrid (until the marketing people got involved)


We will have to wait until lithium sulfar, lithium air or aluminium air batteries come out before EV with ranges about 40 miles will be cheap.

"Hybrid fan: Battery use in cars is not a zero sum situation."

Every battery factory is running at full capacity and selling all they make. There is no spare producing capacity. Until that changes, yes it IS a zero sum situation.

Besides that, one aspect of this article that really bugs me is the use of "kW" when they should be using "kWh". In other words, a term for battery "power" is being used when they are discussing battery "capacity." Horsepower and range on 1 fill up should never be confused like this.


Yes they are running at full tilt, and as a result there has been a constant stream of announcements of new battery production facilities being built. Not only that, the hybrids in production today don't even use the same kind of batteries (NiMH) as cars like the Volt (Lithium). The only devices competing for A123 battery production is power tools.

I'm getting a little suspicious that people (hydrogen advocates, petroleum industry types and who know who else) are trying to delay EVs using FUD tactics like "peak lithium" (BS) and "lets not build EVs because we need the batteries for hybrids" The last person I heard that argument from was the noted local hydrogen advocate Roger Pham. (gee, I wonder why he doesn't want to see EVs hit the market in any number)


What does "CD mode" mean in this post?


CD = Charge Depleting

hybrid fan

If anyone one can build a better car: Do it. Fun conspiracy theories aside, the MARKET will "decide" what will roll on tomorrow's roads. As it should be.

Because the real world is here, and utopia nowhere.


PeteVE can you give us the link that talks about the new lithium deposits?


here is the link. now please note that i only read this article this morning and got the link from another site myself.



Thank You!


wait, no. let me look again. that wasn't the one.


eventually the cost of batteries will come down, this will erase the premium on hybrids and lower the cost of pure electrics.. I cant wait!

By then I guess the majority of cars sold will be hybrids, and dont assume they will all be economical cars.

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