Friday, December 30, 2011

Chevy Volt--Mechanical Engineer Perspective

Chevy Volt Plug-in Hybrid

1926 Model T tractor conversion


















I took the above photos at the county fair this summer. The Volt and Model T tractor conversion are both the result of ever present engineering compromises that tend to be exacerbated when designing a multipurpose machine. With the Model T kit you could convert your car into a tractor for planting season. Although the idea of combining two machines into one was appealing, the kit was not very successful because the resulting tractor preformed poorly compared to real tractors.

With the Volt, you get an electric car and a gasoline car all in one. The electric car is inefficient because it has to lug around an inert gasoline engine, fuel tank, fuel pump, fuel injectors, radiator, oil filter, muffler, catalytic converter and other attending air pollution devices for when you run out of charge.

The gasoline hybrid mode for the Volt is inefficient because it has to lug around a large depleted battery and  two large electric motors in addition to the gasoline motor and its attendant hardware. This explains its dismal 33 mpg performance for a four-seat gasoline hybrid. The lack of a fifth seat is yet another compromise.



Another example of engineering compromise would be those pocket knives that combine just about anything you can imagine into one handy package. However, none of the tools contained in that knife work nearly as well as a separate tool designed for a specific use. Picture trying to measure something with that knife's ...measuring fish hook remover thingy. This explains why car mechanics and carpenters have thousands of dollars worth  of tools at their disposal instead of just one of these babies in their pocket.






Volt owners can also expect higher than average maintenance costs (lower than average reliability) thanks to the complexity of having two drive systems--an internal combustion engine driving an electric motor that in turn drives yet another electric motor.


Powered by electricity without being tethered to electrical outlets, the Volt does everything a great car does ...?

True to America's modern corporate culture, GM attempted to baffle consumers with BS rather than give them a product that earns its market share with superior engineering and performance (like the Prius and Leaf). To this day, journalists are still lumping the Volt in with electric car reviews instead of with other plug-in hybrids. GM's marketing machine had managed to convince the public that the Volt is an electric car. The latest commercials are an attempt to cool the hype because a small consumer backlash was growing ...not to mention Chevy needed a comeback for this Nissan Leaf commercial (look for the Chevy Volt in it). The gullibility of the American public isn't boundless after all.



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7 comments:

Kit P said...

Do appreciate disrespectful comments from a real mechanical engineer?

I agree that a PHEV is a bad idea compared to BEV but hauling batteries around is just a bad idea altogether from an engineering point of view. At least for the near term future until fossil fuel become scarce. Storing electricity in batteries produced by fossil fuel is a no win. Just use the fossil fuels in an ICE directly.

The other reasons BEV are stupid have nothing to do with engineering just good old common sense. BEV are perfect for those who do not drive very far everyday. However, people who do not drive very far are not the problem if the problem is fossil fuel use.

Russ Finley said...

I don't think a plug-in hybrid is a bad idea compared to an electric car. I would take the plug-in Prius over the Volt if we were a one car family because it costs a lot less, holds five people, will be more reliable, and gets far better gas mileage than the Volt.

As a two car urban family, our Leaf, Prius, combination are about as energy efficient as you can get. We spend about $2,700 less annually on car transport energy than the average American two car family.

My wife actually drives about 20% more miles per year than the American average, and I drive about 20% less.

Storing electricity in batteries produced by fossil fuels is a push because electric cars are so much more efficient than gasoline cars. The hope is to bring on line more power sources (a nuclear enhanced renewable grid) that won't rely as much on fossil fuels so we can avoid their negative ramifications.

alain said...

" Storing electricity in batteries produced by fossil fuels is a push because electric cars are so much more efficient than gasoline cars. "

Depends.

take the typical US coal plant achieving a measly 45% energy conversion from coal to electricity at their exit transformer station.

then add another 8% loss during wire transmission from the power plant to your home socket.

then assume that the battery electric vehicle converts the socket electrical load for 65%, since you still have mechanical and tire friction and battery heat loss during load up.

So your energy end conversion from coal to your tire is :

0.45 x (1-0.08) x 0.65 = 0.267 %, meaning 75% of the energy contained in coal is lost forever, even when using a battery electric vehicle.

The most efficient mass made ICE cars achieves 20-25% energy conversion efficiency.

In other words, if you truly want to be energy efficient, load up your BEV with renewable energy sourced from cheap hydro, wind, biomass and home solar PV panels.

Kit P said...

“We spend about $2,700 less annually on car transport energy than the average American two car family. ”

It statements like that ensure that I will not respect you Russ. Especially an engineer because it shows a lack of critical thinking. I do not pick my choice of POV based on averages but on the needs of our family. The way to save money and fuel is to buy a less expensive car and drive less. We can not save $2,700 because we do not spend that much.

What negative ramifications? As an environmental engineer I think people who claim to me environmentalist to explain them to me. What people like Russ want is to put windmill in my backyard and not his.

“Depends. ”

Reading that I was surprised that Alain did a good job on the calculation.

Very few places have excess power capacity that is not fossil. The PNW shuts down fossil plants for about 4 months a year because of hydroelectric, nukes, and wind can meet demand. Of course the reason for the excess capacity in the PNW is heavy industry has been driven out of the area by higher average energy costs.

Since I work in the power industry, I would like to see more BEV but it would be unethical for me to promote it without saying that I is not a good way to either save money or protect the environment.

Russ Finley said...

Good comments Alain.

You are right that an equivalent sized electric car will consume about the same amount of energy as a normal car (which is what I meant when I said they are a "push" in that respect).

They consume different forms of energy (oil verses hydro, wind, solar, natural gas, nuclear, and unfortunately, coal).

We also agree that we need low carbon sources of energy to charge them with, although, I would add nuclear to your list of sources.

Herm said...

The Volt is actually a fairly efficient car even in the hybrid mode.. it achieves 37mpg in the combined cycle per EPA testing. By comparison the similarly sized Cruze has 6 models that range from 27mpg-33mpg (33mpg for the Eco model with a stickshift)combined. The Volt is a nearly 4000lb car running on an 80hp gasoline engine, has decent sporty performance in all modes and can cruise at 100mph all day.

The part that few other cars can match is that in the Electric mode the Volt does not use one drop of gasoline (except in artic conditions).. and for most Americans they can do their daily commute on low cost domestically produced electricity.

Yes it is an expensive vehicle.. perhaps you would be better off with a 2 year old Camry fueled by Saudi oil.

Russ Finley said...

I just fired up a spreadsheet and it's a fact that a Volt will use less gasoline than a Prius as long as you don't drive it more than about 100 miles a day. That's pretty good. Very few people do that consistently.

The problem for me is the complexity and price tag that it took to pull that off.

You can buy a Leaf and a Yaris for a the price of a Volt. The Yaris holds one more person and gets about the same mileage as a Volt after 100 miles and it isn't even a hybrid.

Cost is another engineering compromise, and you can't ignore it, except maybe with airliners and space shuttles ; )