calculation details of Volt's 230mpg city estimate

On the flip side, a PHEV Prius will have parasitic drag from the mechanical transmission reducing its range in EV mode. Neither system is perfection. The series arrangement has an advantage of flexibility. Ships use it to allow optimum placement of the genset for ship balance. In a car, you place it for optimum cabin or battery space. That can't be done if you require a mechanical path between the engine and wheels. It also allows the exploration of internal and external combustion engines, which wouldn't work in directly driving the wheels, but can be more efficient fuel wise. When battery tech improves and prices come down, it is a lot simpler converting a series hybrid to full electric.

 

I am not here to defend GM's history. Its pretty bad. And like Charlie Brown getting the football pulled at the last moment there is a chance of it happening again. But something is different this time......


GM seems to really be behind the Volt concept. I was around during the EV1 days and they were not this into it. They built the EV1 out of super expensive materials and had it pretty much set for a hand made build. That is not true this time, they are going with pretty normal high volume produceable parts, a very standard body and reasonable goals.

The only real tough part in the Volt is the battery. The electronics and computers once figured out are going to be easy to make. Same with the body... genset.... interior.... you name it.

The same is true for the Prius too.... Its the battery!

 

Nothing I've seen suggests the Volt will really get anywhere near 50 mpg in charge sustaining mode. I have seen various things that try to trick readers into believing that, but when you look at the wording more carefully, far lower mpg figures are apparent. This is not a car optimized to be a 50 mpg Hybrid like the G3 Prius so you are only kidding yourself if you think it will be equivalent when running in its secondary mode. Caveat emptor, plausible deniability, suspension of disbelief...they all come to mind when listening to Volt speculation. There are plenty of folks who want to believe the higher values, but based on what I've seen so far, I believe they will be sorely disappointed.

On things hyped like this one has been, it's a safe bet that it will under deliver.

 

ICE combustion cycle will play greater role for MPG in CS mode. Atkinson cycle is about 15% more efficient than Otto cycle due to less thermal loss.

- Civic Hybrid with 1.3 liter Otto cycle ICE gets 45 MPG (highway). 100% pure mechanical power to the wheels.
- Prius with 1.8 liter Atkinson cycle ICE gets 48 MPG (highway). Combination of mechanical and electrical power to the wheels.
- Volt with 1.4 liter ???? cycle ICE would get ?? MPG (highway in CS mode). 100% electrical power to the wheels.

If Volt were to use Otto cycle ICE as the range extender, it should get less than 45 MPG. 10% conversion loss would put it at 41 MPG. If RE can run on the most efficient RPM and make up for the conversion loss, it would still top at 45 MPG. That's just the highway MPG. City MPG may be worse.

 

I think it is highly unlikely that the mechanical to mechanical losses will be anywhere near 2% or even 5%.

The motor/generator efficiency on the Prius peaks at about 93% with more typical values inthe 80-90% region, AC Propulsion only claim 86% for theirs (peak of 91%).

http://www.acpropulsion.com/tzero/AC150_Gen2_specs.pdf.

Putting a generator and motor in series will then result in a best case of about 73%-86%.

The electronics are getting better and the inverter efficiency alone is probably in the 96% region but it is difficult to get an efficient motor when there are extreme weight/space/cost considerations.

kevin

 

Large systems for ships and locomotives have the advantages of scale and few limitations on weight.

I agree that the mechanical losses on the Prius seem high but many of those losses are not just in the mechanical path from the ICE but will also affect a pure serial system (e.g. drag in the final drive).

kevin

 

I'm a brand loyal consumer and I love my Prius.

However there seems to be a little energy here slamming an American auto mfg that is making a very bold move to get us to an alternative way of travel more efficiency.

I respect and support any manufacturer that makes a sincere effort to offer a product that ultimately benefits the United States of America.

As far the “real numbers” go with the Volt, at this point I say let the chips fall where they may. The American public will respond accordingly.

Let’s encourage innovation, after all that’s what makes America great.

 

I don't care if it did get what it is advertised to get. I still would never buy it just because it is a Chevy.

 

I would buy a volt if some conditions are met. I don't like the whole 4 seater deal. occasionally I do transport 5 people. I feel that a lot of the price is inflated, especially since the body is based on a cruze! I know I know that the chasis is the cheapest part of a car, but really makes me think about quality.

 

Bold and [] mine.
I fully agree with the idea of encouraging innovation.
I have visited Saturn dealers pretty much annually up until last year asking if they had any word of a return of the EV1 or other electric car.
I have written to both Saturn and GM informing them I would be interested in purchasing an electric car from them.
I have seen GM crush their working EV the moment they were no longer required to sell EVs in CA (as did some other companies).
And I have yet to hear ANY hint that GM is planning on making an EV.
The key word in your post was 'Sincere'. And I don't believe GM is Sincere.
Meanwhile, in the next 0-3 years we will have EVs from Nissan, Think, Tesla, Karma among others.
When GM actually delivers an EV, I will give them full credit, and even buy it IF other companies don't make a better one.
GM EARNED my skepticism. And it is perfectly possible for them to EARN my business again. But promises won't do it, I need to see the product.

 

1) Just because (pre & post banko) GM is headquartered in the U.S. does NOT mean the 'company' is a U.S. company. When a significant amount of assembly & sub assembly is done in Mexico, Canada, and China, it is simply an auto manufacturing company. Even GM's primary source for batteries (a substantial part of the Volt) appears to be going to China.

2) Sincere? When GM refuses to admit to having a waiting list of thousands for the EV1 (until until the list was WAVED in their face, and at that point they had to spin 'truth' a different way)?

3) Benefits America? When did GM want to benefit America. GM benefits GM. Period. GM, for example left hundreds of acres (multiple manufactuing sites, in multiple states) of abandoned toxic waste ... and that does not benefit America:

New GM Shirks Responsibility for Old Toxic Dumps and Mercury Disposal | Hybrid Cars

Then there was the crushing of the Trolly system several decades ago, but no need to beat a dead horse.

I hope the Volt (If in fact it ever really gets into real numbers production) is a smash hit. If it is, then maybe you can make a ribbon out of a pigs ear.

Even as the Nation has less & less fossil fuel to waste, GM's primary dog & pony show (profitible lines) are Caddies and big trucks. Our nation is over a decade older since hybrid production began. Much of that time was spent by GM pooh pooh'ing hybrids & EV's as PR stunts. If things have changed, why did GM re-higher Mr. Lutz ... who is most famous for recently stating that global warming is a "...crock os $h1t ..." . When corporate leadership says that, and says EV's & hybrids are PR stunts (forcing them to "Go PR" too) then what does that say? Leadership like that? ... I just don't know.

.

 

Re: "Just because (pre & post banko) GM is headquartered in the U.S. does NOT mean the 'company' is a U.S. company."

Oh really. Imagine that. GM is not a US company anymore. And no one told us taxpayers we were bailing out a foriegn owned company. You would have thought the Chinese union workers would have mentioned something.

Re: “Benefits America? When did GM want to benefit America.”

Ok, with a comment like that I realize I’m dealing with an economics genius here. Sorry, case closed. You win.

 

jeeze, so much hate for GM here.i know MANY people (including myself) who have had no major issues with there GM cars and trucks. i better stop now before i say something and get banned os anything

 

You can run a diesel on diesel, bio-diesel, plant-based oil, CNG...I'm just sayin'. Besides 50-mpg isn't all that special. GM was getting that from diesel Chevettes in the 70's.

 

When (if) I buy another car, I'll at least see what Ford is selling in hopes of buying local, if the car really is local and not simply rebadged or mexican. GM ? Chrysler ? Not even on my radar, except when I think about all the taxpayer money wasted.

 

If 50 mpg is not that special, then please explain why only ONE car that can be bought today offers it.

I do not know, maybe that 70's diesel Chevette was a smoke belching tin can on wheels ? What do you think ?

 

If you want pure mileage, then a diesel Chevette or Geo metro will suit you fine. All without the complicated electrical systems needed to push a hybrid. You will notice that over half of the top ten best selling cars in the US are fullsize trucks, large cars or SUVs. People want what they want. And, apparently, they don't want subcompact hybrids.

 

Unholy1, the question still remains.
Where are the cars for sale today that offer 50mpg or more?
Sure, you can modify cars, but few of the public are interested enough, or capable to doing so.
The idea of the Volt is a great step forward. In my mind, it is a step past the current technology IF they can deliver what they promised.
However, GM's track record is poor when it comes to new technology in the last 15 years.
For you to say 50mpg is nothing special when no domestic auto company offers one 'off the shelf' seems a bit disingenous?

 

The point, is that 50 mpg in a 70's Chevette diesel is not the same achievement as 50 mpg in a Prius. The Prius is faster, heavier, safer, and cleaner. The 70's Chevette could not be sold in the US today. And this is before we remember that 50 mpg EPA rating in 1970 would be a lot less today.

See why Prius is special ?

 

I just read this week that journalists were allowed by GM for the first time to take a long enough trip to report on CS mode fuel economy. The author I read posted 32 mpg.

32 mpg