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The problem with this overly simplistic analysis is that it seems to assume that the engine will be running continuously and in the same manner as a conventional vehicle. With the plug-in series hybrids that are being worked on now, the engine will not in fact be running during most of the operation of the vehicle. The batteries will provide sufficient capacity to cover most of the period with grid power.

Secondly a series hybrid engine will be running at constant speed and load and can be optimized for that duty cycle. That means that it can actually be made to run at higher efficiency than an engine that has to be able to smoothly handle operation for 600-6000rpm. The overal efficiency of the whole system can be dramatically increased.

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The Volt is NOT primarily a “series electric” car and it is NOT a hybrid! The Volt is a BATTERY ELECTRIC CAR with a RANGE EXTENDER because the PRIMARY power comes from the electric grid. The 40 mile battery electric range will completely cover over 80% of ALL daily commutes. The primary purpose of the “range extender” is to help the average driver feel comfortable with the fact that they won't be left in the middle of nowhere with a dead battery. This fact will make it GENERALLY accepted thus far superior to the EV-1 or any pure electric car! GM has stated that the future is electric. However the AVERAGE driver must be made to feel comfortable with electric drive. It’s a paradigm shift. The Volt BEV and all PHEV’s for that matter are but the NEXT logical step the FULL electrification of personal transportation.

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Evan Boberg is right. This is exactly why parallel hybrids have been used thus far, because they have fewer energy conversions -- and associated losses -- than a series hybrid. Other factors being equal, the parallel system will win on efficiency.

Sam Abuelsamid is also at least partly right. A series hybrid does, in theory, allow you to use different kinds of engines which are more efficient than the conventional gasoline engines but cannot be used in conventional non-hybrid cars because they don't respond well to being throttled. In a series hybrid they can run at a constant full-throttle condition, or be shut off completely when they aren't needed.

So, why haven't car companies done this? Why didn't Evan Boberg take this possibility into account? It opens a whole can of worms: what kind of engine *are* you going to use, then? Gas turbine? Wankel/Rotapower? Stirling engine? There are several possibilities, but none of them are proven in automotive applications. Car companies have huge capital resources and knowledge invested in conventional piston engines, so they obviously want to use what they can pull off the shelf.

Next point. . . Sam says PHEV serial hybrids, with plug-in charging, change the balance. Yes. . . If you can run part of the time, or most of the time, off grid electricity, then that's a huge boost to your efficiency. But Evan Boberg doesn't address that. His experience in the auto industry was some years back, and Li-ion cells were not in the picture yet, so he probably had no reason to think about PHEVs or factor them into his argument.

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You gain efficiency over regular gas engine because you lose the transmission. Warm up isn't an issue, because the series engine has to warm up also.

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Tim, if you don't think the Volt is a PHEV then I don't know what is. If you go down the Volt's projected specifications, they read exactly like the wish list of PHEV advocate groups like CalCars, Plug-In Partners, etc. It's as if GM took the PHEV recipe these groups had been calling for and copied it word-for-word.

You wrote, "The Volt is a BATTERY ELECTRIC CAR with a RANGE EXTENDER because the PRIMARY power comes from the electric grid." Yes. That is exactly what a PHEV is. That's the definition of a PHEV.

GM: "It's not a tree! It's a large, woody, perennial plant! Unlike trees, it has a single stem or trunk growing to a considerable height and bearing lateral branches at some distance from the ground!"

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Ablert asked "What impact does regenerative braking have on his numbers?"

I did not mention it but he says his example does not include regenerative braking.

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I would have thought that a series hybrid would be more efficient than a parallel hybrid for the following reasons:

1. The engine used in series hybrid does not need to be built for huge sudden loads, such as pulling away from the lights, so can be much smaller, lighter and therefore operate more efficiently.

2. The smaller engine would itself be lighter than an equivalent ICE, making the vehicle more efficient.

3. The series ICE would be able to run at a constant load, so could be perfectly geared and tuned for maximum efficiency, as opposed to a parallel hybrid's ICE, which must rev through a range within each gearing.

4. There is a weight saving over a regular hybrid, because the gas engine does not need to be couple to the wheels.

Additional, series hybrid would be more efficient than an standard ICE car for the following reasons (shared with parallel hybrid):

5. Can reclaim kinetic energy using regenerative breaking.

6. Part of the journey can use energy derived from the grid, which is way more efficient than a self-contained ICE.


And to top it all off, the multiple sequence of efficiency ratios he mentions simply gives more opportunity for improvement, whereas existing ICE cars have only one area for efficiency to improve (actual engine efficiency), which has already been flogged to death for the past 100 years.

eg.
.28 X .95 X .95 X .95 X .80 = .19, but:
.29 X .96 X .96 X .96 X .81 = .21

, and that only assumes a 1%(!) increase in efficiency of a small, perfectly geared, constant speed generator, over a large lumbering, 800 - 6000 RPM 200kg standard ICE engine.

Welcome back, Santa...

Luke Coverdale

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Tony- A Plug-In "Hybrid" will not run at ALL speeds (up to 120 MPH) WITHOUT an operating ICE. Name ONE that will...

The Volt doesn't NEED the ICE for the average 40-mile HIGHWAY commute.

Yes, there are a lot of bushes that look like trees. NO, spiders are NOT insects or "bugs and the Volt is not a “Hybrid.” It’s a BEV with a range extender.

Just because a dog has 4 legs, doesn’t make it a horse and a house cat is NOT a lion.

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Things missing:

Mechanical Transmission losses for the regular automobile.

That any serial hybrid is likely plug in hybrid which improves the numbers.

When running with the ICE on, you don't need to include battery conversions in all the efficiency calculations. It can be generator-> electric motor.

Increased efficiency from running the hybrids engine in most efficient range.

Using alternate generation engines that are more efficient than automotive ICE.

Regen braking and stop and go savings. Which is big, this is where current hybrids get most of their advantage.

In short: of course if you treat the series hybrid as nothing more than an transmission/drive shaft replacement, you are not going to see an increase in efficiency.

The whole point is to open the door to a range of possibilities unavailable without being hybrid, like plug in, regen braking, or things not available even in parallel hybrids like replacing the ICE with something more efficient at electricity generation.

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Sounds suspect to me, but even if this fellow was right,(which he isn't since he neglects several of the major benefits of hybrids, and seemingly ignores real life examples like heavy duty train engines,) it would still be in our interest to pursue cars like these.

Electric drive allows the transmission to be done away with, removing a great deal of inefficiency and complexity, increasing reliability. Electric motors require next to no maintenance, and even the supplemental ICE will run at very controlled, optimized loads and speeds, which I imagine will stress the engine much less.

Safety applications are plentiful when you consider electric, independent AWD. No differentials to worry about, and you can computerize the power distribution for optimal stability, speed, traction, whatever. There is an electrified MINI that has the equivalent of VSC or EBD, except rather than just removing power selectively, it can apply power too. You have the benefits under acceleration, and I imagine being able to turn a certain wheel at any time could have benefits for braking, also.

When you throw in all the efficiency benefits like regenerative braking and charging from the grid, it's a no-brainer. I'm excited for a Volt 2, with ultracapacitors, and shortly thereafter a Volt 3 running on ultracaps alone, and chargeable in 5 minutes.

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Can someone confirm these back of the envelope calculations?

A series hybrid that needs say 250wh/mile travelling at 70mph will need 17.5kW of power. Taking the 86% combined efficiency of the electric drive system that means you need a bit over 20kW (say 25kW just to be on the safe side).

That’s a 34bhp engine to get you from A to B compared to maybe 100+bhp in a conventional car. How can that not be more efficient? Or are my calculations screwy?

Also does he give any reasons why diesels are not possible?

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All things aren't equal.

A parallel hybrid has an ICE much smaller than the non-hybrid model.

A series hybrid would have one even smaller than that.

And it would be tuned specifically for efficiency in producing electrical energy (not mechanical).

I'd think the characteristics (e.g. capacity) of the battery pack would ultimately drive the specs of the ICE "range extender" on your series hybrid.

Hmmm...would an air-cooled diesel work? (no radiator, no spark plug)

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Adding to Luke's and others' comments above, I'd like to offer a few observations:

- A series hybrid could easily halve the output and displacement required for an equivalent-size non-hybrid. The Volt uses a 1.0L, 75hp genset; a Cobalt uses a 140hp 2.0L. This alone would boost the comparative efficiency far above that of a regular vehicle or even parallel hybrid.

- If you start talking about exotic forced aspiration, modified cycles, and optimized combustion regimes (HCCI or DiesOtto for example) you gain yet more efficiency.

- There are other types of engine that could provide motive power to the genset that are very efficient - Sterling engines or even steam cells come to mind.

- It's unavoidable that cars are going to have to start losing weight. Simply pressing the body from ultra-high tensile steel would lighten it by 20 or 30kg. Start talking about composites, and you're talking dramatic weight savings that would reduce the overall amount of energy required to move a vehicle.

- And let's not forget aerodynamic improvements. A significant chunk of the energy-to-the-road is just used to punch a hole in the air. Just slapping a belly pan on a car gains you a few MPG.

Overall, this sort of simplistic analysis only scrapes the surface of the problem. It's excessively limited and doesn't take into account technological and process-related efficiency gains that could far outweigh that 1% penalty.

And one more thing - this is a disgruntled former employee of an American car company. He may be basically correct - but let's not forget that he's not objective and he's got his own dog in the fight.

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I can't name a PHEV that will reach 120 MPH on battery power alone because nobody has made a PHEV of any kind yet, aside from experiments or concept cars. Honda hasn't made one, Toyota hasn't made one, GM hasn't made one, nobody has produced a PHEV for sale (or lease!) to the public. Toyota and GM (here I am referring to the Volt) are the only companies which have announced any kind of plans to produce PHEVs. The only PHEVs on the road today are homebrew Prius conversions.

You insist that the Chevy Volt is an electric car with a range extender. If you take an electric car and add a gasoline-powered range extender, then you don't have an electric car anymore: you have a PHEV. That's what a PHEV is -- it's just like an electric car, except it has a "range extender" powered by some kind of fuel.

But ultimately the Chevy Volt is powered from two energy inputs: grid electricity and gasoline. That makes it a hybrid. There's no way you can classify it as a true electric car, a pure electric car, when it's not powered purely by electricity.

Why does this matter? It matters because GM are very intentionally trying to sow confusion. (And apparently they are succeeding.) They *want* the press and the public to be confused about the difference between PHEVs and BEVs. They want the public to think what they are selling is the same thing as a Tesla Roadster or a Phoenix SUT. They want to take credit for bringing back the electric car, but without all the expense and risk of actually producing electric cars.

GM's marketing dream is that in 2010 you'll go shopping for a new car, and you'll be looking at the Chevy Volt and the Tesla "White Star" and you'll think they are the same thing, they are both "electric cars". The Volt will be cheaper, and you'll buy it. In order for this to happen, the term "PHEV" has to be erased from the lexicon, and the term "electric car" has to be stretched to include cars you put gasoline into. It's wrong.

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What impact does regenerative braking have on his numbers?

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Snark, your calc' on efficiency of smaller engines is not that simple. Explain why a 2.2L passat gets better mileage than a 1.6L miata? A lot of minivans with V6s get pretty respectable highway mileage (low 30s), but the 4-banger versions of the same van need to run at higher RPMs and so burn more gas. Smaller engine does not always mean more efficient, it means bigger thermal loss. It really all depends on how the small engine is coupled to the generator... if they screw up the gearing, the engine will be running at high RPMs and will burn more gas.

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Tony- You said, "But ultimately the Chevy Volt is powered from two energy inputs: grid electricity and gasoline. That makes it a hybrid."

This would make it a hybrid IF it were true. However, this is NOT TRUE when you commute less than 40 miles.

Anyway, we're picking nits. A series electric car is more efficient when in a plug-in configuration. This MAY not be the case without the plug-in capability unless electric motor mass/efficiency ratio has improved since January 2004 when this book was written. I believe that many improvements have been made in the last 3-1/2 years. Include these motor improvements with the other series attributes mentioned in the other posts here and e-flex is far superior to parallel hybrids in light duty automotive applications. It is NOT a catch all silver bullet.

Call it what you like, but it’s GM’s baby so they have the right to name it.

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"Explain why a 2.2L passat gets better mileage than a 1.6L miata?"

Gearing, primarily, and the engine is under less stress to rev high to propel the vehicle down the road. The Passat uses direct injection, as wellOh, and the Passat is 2.0L, not 2.2, just FYI.

"A lot of minivans with V6s get pretty respectable highway mileage (low 30s), but the 4-banger versions of the same van need to run at higher RPMs and so burn more gas."

True, but this isn't because of something inherent to the engine, it's because the engine is working harder to motivate the vehicle. The lower-powered engine has to be caned harder to move the vehicle. The APU/range extender/genset (whatever you want to call it) of a series hybrid isn't working to motivate the vehicle directly, it's merely spinning a generator and is running at constant load and RPM. It's not revving hard, it's not transmitting power directly to the road, it's not being revved up and down, and it's not burdened by a flywheel. Running at optimal RPM, under constant load under the conditions of a series hybrid, a smaller-displacement engine is always going to be more efficient than a larger one.

"It really all depends on how the small engine is coupled to the generator... if they screw up the gearing, the engine will be running at high RPMs and will burn more gas."

This doesn't follow, friend, sorry. The gearing is a function of the transmission - which would be absent in a series hybrid. A series hybrid generator would simply be a generator attached to the output shaft of an engine, with no gearing whatsoever. The RPM of the engine is simply determined by what the ECU tells it to do, and even GM techs aren't going to program it to spin faster than it needs to for no reason.

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Re: "Call it what you like, but it’s GM’s baby so they have the right to name it." Well. . . That depends on how you feel about truth in labeling. In the food industry they'd never get away with something like that, the FDA would be all over them. You can't sell "chocolate" that doesn't contain cocoa solids and cocoa butter, you can't sell "ice cream" without cream, etc.

Apparently, in this country you do have a right to sell an "electric car" that fills up at the gas pump. But I also have the right to call B.S. on it.

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