Ronin of the Spirit

Because reality is beautiful.

Chevy Volt analysis

Again with hybrids…

I wrote this blog several times before I was able to figure out what I wanted to say. It is very frustrating. I was trying to gather data to make an apples to apples comparison rather than an apples to oranges comparison. A car is not an engine, or a motor, or power train. A car is a system, and all part have to be analyzed correctly. I just sort of brain puked everything I was learning into a OOdoc and it didn’t make for fun or interesting reading. So here goes my last try.

GM has created a concept car called the Chevy Volt. First a note on GM. General Motors is not in the business of making cars. GM is in the business of making money for its stockholders. They happen to do this by largely by making cars, but like any large organization to effectively do their core task they must be equally skilled at many other tasks, liking schmoozing government officials and probing the public.

The expressed purpose of the Volt is to introduce the E-Flex system. Chevy’s late blooming (but wise) attempt to create a standard component set for hybrids. Wanting to get the most bang for the buck, they also try some new styling cues. You might have noticed I said “expressed purpose” There’s a reason for that. GM is pushing the very edge of promotion to flat out lying. Remember that GM’s job is to make money.

Lie number one: The Volt was created to show off the E-Flex. The car market is about selling crap to stupid people. People do not buy SUVs because they really need off-road ability. They buy SUVs because they think they look cool, and that driving a cool looking car makes others view them as better people. (Thats not my opinion. That’s the statement of the head artist responsible for the Dodge Dakota. He also said he made it look like a big cat on purpose because most people are insecure and driving a car that looked like a Puma would make them feel safe and in control of other people. Interesting, “safety” is one of the primary reasons people sight for buying an SUV even though statistically they are less safe than sedans.) If you think that Chevy introduced a fairly advanced engineering concept to the unwashed public to see what they thought of the engineering, I have a bridge to sell you. In general, people are too stupid to think about engineering. Chevy introduced it to see what kind of an emotional relationship people would form with their poorly understood notion of the engineering. (Example: Correctly designed dual overhead cams actually have a minor performance loss at the low RPMs where most people drive. But people have an emotional attachment to DOHC that says “dual cams means FAST!!!” so they put them in almost everything.)

Lie number Two: The Volt will be ready for production with by 2010. The Volt show car uses a form of battery called lithium ion (called li-ons). GM can’t produce them at a price to sell the Volt. GM hired Compact Power and Continental Automotive Systems not to produce the battery, but to research it.

Lie number Three: Plug in hybrids offer the best of both worlds: battery electric vehicles (BEVs) and internal combustion engine (ICE) vehicles. It doesn’t. It doesn’t in a big way. Everything I’ve said so far is pretty easy to research. This is where it gets tricky. Theory and practice are not the same, but the people paid to report theory get paid proportional to their ability to make devices that are lab queens (only does whats being reported when under ideal circumstances) sound like something that will be just as happy and functional in your car or home.

EVs (electric vehicles)

Everything you know about electric vehicles is probably false. First of all, BEVs never died. In their own niche nothing else can even come close. Hundreds of thousands of BEVs are made every year. Forklifts are common example. Second, BEVs are not incredibly simple machines. Yes, they are simple in concept. If you want to, you can build one in your garage. If you wanted to, you could build all the part of nuclear reactor in your garage. The fact that you can make the basic components of something doesn’t mean you can get them to work together in an ideal manner for the intended purpose. Making BEVs is easy. Making good BEVs is really hard. Forklifts happen to have a very narrow market niche which perfectly matches the strengths and weakness inherent to the design. Cars don’t. The Tesla roadster is an amazing BEV. And it costs 100 grand. Good design is hard. Paying people do things that are hard takes more money. In the category of hybrid vehicles (for which no one has yet introduced a cleaver abbreviation) they are again, produced by the hundred of thousands. No one has made a direct drive locomotive for 50 some years. All locomotives are hybrid, and the vast portion of the worlds submarines as well. Hybrid technology is not new. Its not different. It is just demanding. Like BEVs, hybrid vehicles are simple in theory, but hard in practice. An older, but common example is a GE Dash 8-40CW, which has Turbocharged, inter cooled split cooling 4000HP V-16 powering an alternator, the power of which is then rectified into DC power to go to not one but six traction motors (one on each axle) Locomotives use this diesel to alternator to rectifier to DC motor system because when the system is big enough, the demands variable enough and the engineering careful enough it yields a fuel savings. Did you notice the “demands variable enough” part? If total efficiency in a lab was the goal, they would NOT use hybrid but direct drive. The problem is that the direct drive which can move an 8000 ton load from a dead stop takes different technology than the drive system that can move it along at 70 mph (the max speed for a Dash 8-40CW)

Chevy’s answer is to combine the incredible complexity of a standard hybrid (Engine, alternator,electric motor) with the complexity of a standard direct drive vehicle (Engine, transmission) and the complexity of a BEV (battery pack, controller, electric motor) Giving us a vehicle that has…
1 engine, 1 transmission, 1 electric motor, 1battery, 1 controller, and 1 alternator. The transmission, by the way, is the most overworked part, responsible for making sure that the engine’s power is either charging the battery or moving the car or both at some infinitely variable ratio of action. And the batteries don’t exist yet. But if they did, they would have an effective power density of 1/24 that of gasoline. That is to say, the car gets 50 MPG of gas, but only 2.08 miles for a fully charged battery of a weight equal to said gallon of gas (That figure took me about 3 hours to pin down, by the way.)

The Toyota Prius is a hybrid of the same vein. It gets 46 MPG which is heralded as the best ever sold in the US (which it isn’t). However, a major college recently did the math. When the Prius’s “radical” drive train is removed and the original engine powers a standard 5 speed transmission it actually gets better mileage. ( This is due to the removal of over half a ton of bulk: the batter pack, alternator, special splitter transmission, and 2 electric motors.) There is no reason to believe the Chevy Volt will be any better.

The final lie is not so much about the Chevy Volt, but about the whole save-the-planet-by-driving-electric-cars crowd. This is a bit mathy, but simple if you pay attention.
Your standard car engine is, in practice, about 25% efficient. Then through a 92% efficient transmission. (There are other loses, but they are the same for both electric cars and ICE powered cars so they don’t figure into the comparison.)
.25 * .92 = .23
Battery powered car has power going into 95% efficient controller, then an 85% motor.
.9
5 * .85 = .81
But how does an electric car get its power? Around 60% get power from coal fired steam plants (30% efficiency on a good day) Then then through miles of copper wire and transformer (97%) then through a 95% effiecient charger, and into the batteries (lead acids which are most common have only 65% charging effieciency, but we’ll use the Volts as yet unmade li-ons at 99.9%)
.81 * .30 * .97 * .95 * .999 = .22

Since the drive train of an charged electric vehicle begins at the regional power plant, the total efficiency is 22%. One percent less than a well made car with a stick shift. If the EV in question uses lead acid batteries this is a paltry 15%!!!

The Chevy Volt is a well marketed excuse to sell people a very complicated, poorly performing machine which actually uses more fossil fuels to go the same distance. Car which get better economy with less compromise are manufacturable, but not nearly so profitable. And the public is swallowing the BS with a smile.

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November 25, 2007 - Posted by | Uncategorized

2 Comments »

  1. A professor once told me an interesting quote. “There are lies, damn lies, and statistics.” You are right in that it is difficult to make apples to apples comparisons here, and consequently I believe that your efficiency comparisons are flawed. For instance, if you’re going to go all the way back to the power plant to look for efficiency losses for an EV, then you also need to go back to the oil refinery for efficiency losses for the combustion vehicle.

    The best way I can think of to make these kinds of comparisons is to look at the almighty dollar, because any corporation will pass on the costs of production inefficiencies to the consumer. The Chevy Volt can run for 40 miles on a single battery charge before the IC kicks in to recharge the battery. Depending on the cost of electricity where you live, recharging the battery will cost between 50 cents and a buck for those 40 miles. Driving those same 40 miles with a highly efficient IC vehicle will cost approx. $3.00 (assuming 40 miles / gallon with current gas prices around $3.00.) So the operating costs of even the best IC vehicles out there won’t be nearly as cheap as the EV.

    On other errors in your post, the Volt’s IC engine is not connected to the drive train as is the current Prius model. It serves only as a generator to recharge the battery. Chevy makes a point in calling this engine a “range extender.” This eliminates much of the system complexity you mentioned. A transmission may not even be necessary in the Volt due to the high torque of the direct-drive electic motors, but that is debatable.

    One point I do agree with is Lie #2. I doubt GM will be able to get this to market by the end of 2010. As an engineer, I’ve been given too many agressive production deadlines by upper management to know that they’re invaribly unattainable.

    Comment by Thanyon | November 26, 2007 | Reply

  2. The reason that I think its acceptable to go back to the power plant with electrics, but not the refinery with gasoline is because I am going back to fossil fuels in both cases. As I said in my later post, the cut off line for pollution is 80 MPG. If you can make a gas burning car get better than 80 MPG you will make your power in the car with less pollution at the tail pipe than the smoke stack. You are right about the cost, but only partially. Yes, 40 miles worth of electricity costs only 50 cents. Coal costs about 2 cents per kilo, a kilo of gasoline costs about a dollar. Gas has 1.5 times more energy. So one dollar can buy you either 44.4 MJ of energy in gas OR 976.8 MJ in coal. But turning coal into electricity and running that electricity thousands of miles from the plant so kills the efficiency that as I said at 80 MPG is the cut off point. And direct linkage is more efficient at some RPMs than genset motor linkage. My complaint with the prius is the complexity of this linkage.

    Comment by oneliterofmight | November 28, 2007 | Reply


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