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Plugging in the Feds: The New Hybrids

By Chris Ellis

What a future drive train on a 'Mk II' Volt might look like.

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Saab BioPower 9X Hybrid Concept
PHOTO CAPTION: Saab BioPower 9X Hybrid Concept car debuted in 2008. It is currently powered by 200 hp, 1.4-liter flexible-fueled engine mated to GM's 'next-generation' hybrid drive.
Open Access Article Originally Published: November 06, 2008

President-elect' Barack Obama has promised that 'half of all cars purchased by the federal government will be plug-in hybrids or all-electric by 2012.' Some of this requirement can be met by Chevrolet Volts and plug-in versions of the Toyota Prius, but there is a need for plug-ins which can offer more, in terms of both size and performance. This article describes a generic powertrain for sedans the size of a Chevrolet Malibu, Ford Taurus or Dodge Charger and larger, and for all sizes of SUV. The article starts with the specification and then offers explanations for the various choices.

The plug-in battery pack needs to be modular, to provide users with a choice of AER (All-Electric Range), from some 20 miles at city speeds to over 60 miles on freeways at the legal limit. Assuming an average electricity consumption of 250 Wh per mile in the city, the available capacity of the smallest pack needs to be 5 kWh. Because the state-of-charge swing needs to be less than 75% to improve battery life, the nominal battery capacity will be around 7 kWh. The battery pack will be located under the trunk floor, in what was the spare wheel well. Consequently, run-flat tires will be fitted as standard.

The base engine could be an E85/gasoline version of a small I-4, similar to the 100 bhp unit in the Volt. The optional more powerful engine might be a turbocharged version of the same engine, producing some 150 bhp on gasoline and 180 bhp on E85. Perhaps surprisingly, the more powerful engine should use less E85 than the base engine when cruising because it will have properly implemented flexible fuelling (see Saab BioPower), unlike most other systems claimed to be optimal. Most systems adjust ignition and injection timing, but Saab uses variable boost turbocharging to modify the effective compression ratio to take full advantage of the higher octane rating of most biofuels. The result is that the 'mpg gap' between gasoline and E85 can close to the point where it costs less per mile to use E85.

The engine will be connected to the front wheels via a dual-clutch transmission (DCT), which combines the efficiency of a manual transmission with the ease of use of an automatic. The engine and transmission will be mounted in the conventional transverse position, under the hood. Because the DCT operates here as part of a parallel hybrid configuration, engine power can normally be delivered even more smoothly than a DCT or conventional automatic operating on its own.

Hykinesys Malibu drive train with PowerBeams

The 'foundation technology' for the powertrain is a surge power unit, mounted inside the transmission tunnel down the centerline of the vehicle. The Malibu, Taurus and Charger are already available with a conventional 4WD system requiring a transmission tunnel which is large enough, with some minor fettling, to take a surge power unit. The surge power unit will, in its basic form, drive (and be driven, during regenerative braking) by the rear wheels, via the rear final drive. The sketch indicates where the key components will be located in the vehicle. The surge power unit will have an available energy capacity of some 500 Wh, with a peak output power rating of over 260 bhp (~200 kW), and be kept topped up by the plug-in battery, and the engine when the battery is flat. Most importantly, the surge power unit should have the ability to return over 60% of the kinetic energy of the vehicle during a full brake/accelerate cycle. This contrasts with the less than 35% returned by most current hybrid drives. For the FBI (and police?), a more powerful version should be available which the front as well as rear wheels, via a 4WD version of the DCT. Cars with V-8 engines will become so 'last millennium'.

It will be clear from the above that an electric-only version (BEV) could be achieved by replacing the engine and DCT with an additional battery pack in the engine bay. Another option will be to omit the plug-in battery, leaving the surge power unit to support a very effective 'fuel-only' hybrid version. Imagine how attractive this will be in countries like Brazil, where ethanol is cheap and produces little net CO2.

Because the base plug-in battery pack doesn't have to absorb surges of regenerative power or support peak acceleration, it needs to deliver or absorb no more than 25 kW continuously, allowing a choice of battery chemistry optimized for energy density and least-cost-per-mile, rather than peak power. The low power requirements will also help ensure long battery life.

In principle, the surge power unit could be based on a high-power motor/generator and battery (or ultra-capacitor), or a hydraulic system or one based on kinetic energy storage. Kinetic energy storage (i.e. using high-speed flywheels) is theoretically the most promising in terms of efficiency, power and, ultimately, production costs, and is expected to be used in Formula 1 racing next year. It may well be that the American Le Mans Series, with it new Green Challenge, will become the crucible for the kit that the likes of Scully and Mulder may be driving by 2012.


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5 comments so far...

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Posted by: jim stack:

  While I appreciate your attempt, I really don’t like the analysis, conclusions, and design tradeoffs of this article.

1. The assessment that a modular battery pack is needed may not be correct. The only benefit of a smaller battery pack is to save costs. Smaller packs, however, will require more cycles and it is generally cycle life that kills batteries and thus determines the amount you’re going to have to spend over the life of the vehicle, whether you buy them all at once or replace them occasionally. We don’t yet know what the optimal size is but in the long run, it probably doesn’t make much difference as long as it is at provides at least 50 miles of highway range.

2. Good vehicle integration (not that anyone has done this except for Toyota’s RAV4EV and Prius) can allow the battery to unobtrusively be placed out of the way and not have to replace the spare tire or displace the trunk. Cheesy integration jobs such as the Honda Civic Hybrid and GX just demonstrate that the auto manufacturers really don’t want to spend much effort building alternative energy cars. The benefit of run flats instead of a spare is the weight savings.

3. I agree that a 4 cyl ICE is all that is really needed buy why burden it with a turbo charger. If the ICE is used to provide average load (unlike your view), then it can be optimized to run only at its most optimal RPM and load and thus get much better thermodynamic efficiency that one that has to actually drive the wheels and thus is subject to a highly dynamic and inefficient environment. The electric motor can provide all the surge capability you could ever need.

4. Why carry all the weight, expense, maintenance complexity, and inefficiency of a transmission? The transmission is just a device to compensate for the limits of the ICE. Get rid of that beast entirely.

5. By the statement that 'Because the base plug-in battery pack doesn't have to absorb surges of regenerative power or support peak acceleration, it needs to deliver or absorb no more than 25 kW continuously, allowing a choice of battery chemistry optimized for energy density and least-cost-per-mile, rather than peak power. The low power requirements will also help ensure long battery life.', you are completely missing the strengths of batteries. Batteries absorb power very nicely as long as they stay cool. By the time the Tesla Roadster had enough batteries to go over 200 miles on a charge, it had no problem putting out 275 ft lbs of torque to give it incredible performance, even though the batteries were optimized for capacity. Using capacitors, hydraulic (pneumatic actually), or flywheel surge storage relieves the battery of cycles, thus potentially extending its life or regenerative efficiency. It isn’t needed for surge power with a reasonable sized battery pack.

6. Most engineers DON’T agree that parallel connection is more efficient at highway speeds. They agree that parallel connection is most efficient IF you assume you will be driving using the ICE most of the time because you are driving long distances. For most people’s normal driving, with a decent (~50 mile electric range, ~75 mph electric speed) serial hybrid, they will only light off the ICE a few times per month.

7. This article seems to assume that the ICE will be needed to drive at highway speeds. This is simply because today’s hybrids barely make use of their electric drivetrain. The Volt and strong hybrids should be able to go at full performance on batteries alone, using the ICE simply as a range extender for long trips. Overall, there seems to be a total lack of understand about the electric drivetrain at all. Worse, the article generally gets all the facts completely reversed.

The strengths of the electric drivetrain are that it is fundamentally:

• Very efficient

• Handles wide range of speeds and loads efficiently

• Cheap on a $/horsepower basis

• Can run off of renewable, sustainable energy

• Electricity is easily transported efficiently

• Electric distribution infrastructure is already in place

• Battery technology is improving greatly Its weaknesses are:

• Batteries have low energy density when compared to gasoline (ie they are heavy)

• Batteries are expensive today

• Battery cycle life today is fairly low

The strength of the ICE powertrain are:

• Gasoline has very high energy density

• Gasoline comes from oil which is essentially energy that can be pumped out of the ground

• They are available today at commodity prices

The weaknesses of the ICE powertrain are:

• We are going to run out of gasoline (the only hope is that we’ll die before that happens

• ICE are very inefficient overall (wastes energy and requires extreme cooling measures)

• ICE perform very poorly at slow speeds

• ICE are very inefficient when they need to operate at differing speeds and loads

• Gasoline is highly explosive and very dangerous (thousands of horrifying deaths per year)

• Most gasoline comes from places where the people are psychotic and hate us

• Gasoline is toxic

• ICE creates toxic pollutants

• ICE require a lot of maintenance

• ICE requires transmissions that are very complex (expensive and maintenance intensive)

• Gasoline requires a lot of energy to refine it from oil

• Gasoline/oil is difficult/inefficient to transport from source to use

• Gasoline and Diesel ICE are dirty, causing them to wear out quickly without a lot of effort (oil changes)

Now why would a well engineered hybrid have any more mechanical ICE components in it than necessary?
Posted by: Earl Cox:

  Comment 2 is lengthy but shows only a superficial understanding of both the issues and the proposed solutions, so I will restrict my riposte to just the first two points, about battery size and run-flat tires.

Point 1 would make sense if battery costs remained constant over the life of the vehicle, but this is obviously not going to be the case for at least the next twenty years. Consequently, what makes real sense is to fit a battery with the necessary AER for a typical day, and replace it with an inevitably cheaper battery when it expires. Similarly, the other points don't bear close examination.

Customers opt for run-flats to avoid having to change tires. The weight saving is a trivial bonus, resulting in a small amount of fuel cost saving. But this is an illusion, net, because the replacement run flat tires are much more expensive. Run-flats are mainly about safety and convenience; weight and fuel-cost saving is secondary.
Posted by: Chris Ellis:

  Chris, Thanks for the response. Good point about not worrying about replacing the battery since they hopefully will become cheaper over time anyway. I think you'll find that GM implemented run-flats to reduce weight in the EV1 and then moved them to the 'vette to also reduce weight and increase trunk space. It's only recently that they have been introduced into luxury cars that are expected to be driven by people who would never change a tire themselves anyway. I would like to restate that all of your design assumptions are geared toward getting better mpg, not getting rid of petroleum products. My preference for and interest in EVs is not to just postpone our inevitable depletion of oil but, rather to have a sustainable mode of transportation that will suffice for my grandkids, their grandkids, etc (figuratively speaking of course, since I don't have any kids). Your design trades and emphasis, as shown by this article and your automobile X-prize entry will clearly milk the most out of a petroleum powered vehicle but will never eliminate the need for an affordable, liquid, combustible fuel.
Posted by: Earl Cox:


In comment 4 you restate that 'all of your design assumptions are geared toward getting better mpg, not getting rid of petroleum products.'

That's just not true. Try reading through my article and the links again carefully, with your disbelief suspended, and you will see that I've advocated Plug-in Biofuel Hybrids (PBHs) consistently for years. There's no petroleum at all in a PBH if the lubricants are synthetic and the fuel is biobutenol, as advocated by BP and DuPont. In fact, GM has promised that the Volt will come with a 'flex-fuel' engine as standard, so the Volt is actually a PBH, not just an E-REV.

In Europe, Japan, etc, heavy petroleum-fuel taxes will encourage PBH owners to run as many miles as they can on 'non-petroleum', be it electricity, CNG or biofuel. The incentives are weaker in the US, but they are still there.

I can only assume from what you have written that you have some vested interest in forcing most Americans to drive vehicles which only run on electricity. I would prefer to see them provided with the freedom and flexibility to decide for themselves how they energize their vehicles. They might prefer that as well.
Posted by: Chris Ellis:

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