calculation details of Volt's 230mpg city estimate

[BoostedTimmy]

I've only been a member of these forums for like a week, and only had my prius for 2 days, but I can already tell I will spend very little time posting on these forums....

While half of this thread may be legitimate debate, the other half is just pure GM hatred bullshit. I wish some of you people would finally get your heads out of your asses, GM makes solid vehicles. If you have a problem with the 230mpg rating, whine at the EPA not at GM, you know damn well any company that got a rating like that from the EPA would throw it around all over.

The Volt goes 40 miles on battery, then operates on a mode just like this prius, so why is it so hard to believe it can get 50mpg after the battery depletes?

I can't wait until it comes out, it's going to make the prius look like a gas hog and setsthe bar for what cars should be.

[Shawn Clark]

Originally Posted by Glider

There are many links giving 50 MPG when on gasoline. This one is in the Fuel Efficiency section of this Wikipedia article.

Which is complete bullshit written by Volt fanboys. I tried to correct it using information from GM's own press releases that reveal a far lower value, but the fanboys would have none of that.

[usbseawolf2000]

Originally Posted by BoostedTimmy

.... If you have a problem with the 230mpg rating, whine at the EPA not at GM, you know damn well any company that got a rating like that from the EPA would throw it around all over.

So why did EPA back away from GM's 230 MPG claim?

EPA backs away from GM claim of 230 mpg for Volt — Autoblog

Originally Posted by BoostedTimmy

The Volt goes 40 miles on battery, then operates on a mode just like this prius, so why is it so hard to believe it can get 50mpg after the battery depletes?

It seems that 40 EV miles are for low speed only. At highway speed, the range should be less. Volt's charge sustain (CS) mode is nothing like the Prius. 100% of the Volt's gas power will have to go through conversion loss since there is no mechanical path to the wheels.

We'll see when it become available with reviews.

I still believe the Volt can be a great car if launched at the right time. 2010 is not the right time and it's "foolish" usage of the expensive battery for PR reason.

A 25 MPG non-hybrid would consume 6,000 gallons of gas over it's 150k miles life time.

A 50 MPG Prius would consume 3,000 gallons of gas with a small 1.31kWh HV battery pack.

The Volt has 16kWh battery pack that is over 12x higher capacity than the Prius'. In another word, you can make 12 Priuses for ONE Volt. This way, Toyota is reducing 3,000 x 12 = 36,000 gallons consumption. However, the most the Volt will reduce is 6,000 gallons. The key is wise usage of the battery pack with the affordable mass production price.

[BoostedTimmy]

Originally Posted by usbseawolf2000

So why did EPA back away from GM's 230 MPG claim?

Pre releasing numbers is something that's done pretty often with all auto manufacturers since the EPA testing procedure is widely known, however, since the Volt acheived such high numbers due to it's intial electric operating mode and not neccesarily it's fuel efficiency, the EPA decided a new test should be made for the Volt since it's a competely different type of vehicle.

I just found out I cant post any links for this because I'm to new to the forum, its definately out there though.

It seems that 40 EV miles are for low speed only. At highway speed, the range should be less. Volt's charge sustain (CS) mode is nothing like the Prius. 100% of the Volt's gas power will have to go through conversion loss since there is no mechanical path to the wheels.

I think that low speed only to be determined, but I honestly am not sure. I would think that with such a powerful battery/motor highway speeds would not be an issue? Also, a serious question because I agree with you here....I've pondered since I saw the Prius do it...I would think that there would be a decent conversion loss as well, yet so often I see the synergy drive doing exactly this, not drawing current from the battery but the ICE powering the front wheels AND the electric motor....what is the point in this? Under hard acceleration it seems to draw from the battery so I can't see how this helps in any possible situation?

If the Volt operates like GM claims, it has the possibility to allow most commuters to never use a drop a fuel, which would make up for any number of Priuses you could build.

The Volt will certainly cost MUCH more then the Prius, and there are many factors in whether if ever it would ever be more cost efficient then the Prius (I bet in 90% of cases it wouldnt), but I just love the idea of being able to reduce/eliminate my dependence on foreign oil with an american car, two great things in one

[john1701a]

Originally Posted by BoostedTimmy

I've pondered since I saw the Prius do it...I would think that there would be a decent conversion loss as well, yet so often I see the synergy drive doing exactly this, not drawing current from the battery but the ICE powering the front wheels AND the electric motor....what is the point in this?

With a traditional transmission & engine, you'll get losses from RPM fluctuation. Prius holds it steady more, gaining advantage by routing the excess thrust through the generator. So yes, there is indeed a loss. But the overall result is a benefit.

With the generator from Volt, that is nothing but generator power once you've depleted the battery. And in GM's own words, it's more efficient to avoid that... which was a heavily promoted advantage for Two-Mode.

GM contradicting itself and the ever-changing story is what pushed me to document this particular claim, specifically the 230 MPG. Being so vague allows them to "clarify" later. That's why I'm pushing for detail now.
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[john1701a]

Originally Posted by BoostedTimmy

If the Volt operates like GM claims, it has the possibility to allow most commuters to never use a drop a fuel, which would make up for any number of Priuses you could build.

It certainly seems that way, until you look closer at some numbers. This is what I posted on both the dedicated Volt forum and the big GM forum:



If consumers don't buy a Volt, what do they buy instead?

30 MPG cars will cancel out the benefit of Volt.

Volume is the problem. Consider what's being offered overall. It's easy to see the difference that the small quantity of Volt makes will be offset much easier by a far less expensive 50 MPG car instead.

Volt will optimistically use about 40 gallons of gas for 15,000 miles of travel per year. Prius will use about 300 gallons for the same distance & duration. A guzzler (30 MPG) will use 500.


Consider big picture sales, for 500,000 vehicles...
50,000 Volt + 450,000 guzzlers = 227 Million gallons
250,000 Prius + 250,000 guzzlers = 200 Million gallons


Consider big picture sales, for 5,000,000 vehicles...
200,000 Volt + 4,800,000 guzzlers = 2,408 Million gallons
1,000,000 Prius + 4,000,000 guzzlers = 2,300 Million gallons


Consider big picture sales, for 10,000,000 vehicles...
200,000 Volt + 9,800,000 guzzlers = 4,908 Million gallons
1,000,000 Prius + 9,000,000 guzzlers = 4,800 Million gallons


Notice the pattern?

Even if 1 Volt was sold for every 5 Prius, it still wouldn't be meaningful.

That's why I'm so persistent about GM also offering a lower priced model of Volt. To really make a difference, high-volume is essential, regardless of electric-only range.


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[BoostedTimmy]

Originally Posted by john1701a

It certainly seems that way, until you look closer at some numbers. This is what I posted on both the dedicated Volt forum and the big GM forum:



If consumers don't buy a Volt, what do they buy instead?

30 MPG cars will cancel out the benefit of Volt.

Volume is the problem. Consider what's being offered overall. It's easy to see the difference that the small quantity of Volt makes will be offset much easier by a far less expensive 50 MPG car instead.

Volt will optimistically use about 40 gallons of gas for 15,000 miles of travel per year. Prius will use about 300 gallons for the same distance & duration. A guzzler (30 MPG) will use 500.


Consider big picture sales, for 500,000 vehicles...
50,000 Volt + 450,000 guzzlers = 227 Million gallons
250,000 Prius + 250,000 guzzlers = 200 Million gallons


Consider big picture sales, for 5,000,000 vehicles...
200,000 Volt + 4,800,000 guzzlers = 2,408 Million gallons
1,000,000 Prius + 4,000,000 guzzlers = 2,300 Million gallons


Consider big picture sales, for 10,000,000 vehicles...
200,000 Volt + 9,800,000 guzzlers = 4,908 Million gallons
1,000,000 Prius + 9,000,000 guzzlers = 4,800 Million gallons


Notice the pattern?

Even if 1 Volt was sold for every 5 Prius, it still wouldn't be meaningful.

That's why I'm so persistent about GM also offering a lower priced model of Volt. To really make a difference, high-volume is essential, regardless of electric-only range.


.

Yes but this is assuming that the Volt will infact consume 40 gallons of gas, while it theoretically can cosume ZERO gallons which is more what I was suggesting there. IMO you're also taking what I would consider to be the BEST possible MPG number for a typical Prius driver (50mpg), while 50mpg may be average for this forums I highgly doubt those who arent obsessed with the car typically get quite that. I don't think 40 gallons is optimistic if most owners have <40 mile commutes either, I actually feel that is quite the opposite.

Also, consider that the Volts ICE exists solely to charge that battery, so it will operate at the max efficiency to do so whereas the Prius's motor is not because it's more concerned on where my foot is on the gas pedal.

Consider big picture sales, for 500,000 vehicles...
50,000 Volt + 450,000 guzzlers = 227 Million gallons
250,000 Prius + 250,000 guzzlers = 200 Million gallons

Possibly true, but once again IMO since most people would be using the Volt for their commutes this is still somewhat unfair. Now consider this, we can either buy 250k Prius's and send ALL of that money to Japan, or 50k Volts can be sold and ALL of the money stays here, allowing GM to furthur improve on the design and possibly bring the price down lower as well as boosting the economy.

edit: Before someone points it out, yes I know there are atleast 10 spelling errors in that post and no, I don't care.

[raygundan]

Originally Posted by BoostedTimmy

The Volt goes 40 miles on battery, then operates on a mode just like this prius, so why is it so hard to believe it can get 50mpg after the battery depletes?

The Volt is a great idea, and I'm hopeful that it will be a great car. But it does not operate "on a mode just like this prius," after depleting the main battery-- it can't. There is no physical transmission between the engine and the wheels, so all of the power in "charge-sustaining" mode goes through the engine->generator->motor power conversion losses.

My trusty Civic is still cranking, so I'm waiting to see what shakes out in a year or two in the plug-in market.

[daniel]

Originally Posted by BoostedTimmy

If you have a problem with the 230mpg rating, whine at the EPA not at GM

The 230 mpg figure has nothing to do with the EPA. By the same method, my Xebra gets a billion billion billion miles per gallon because it's pure electric and does not use any gas at all.

Originally Posted by BoostedTimmy

The Volt goes 40 miles on battery, then operates on a mode just like this prius, ...

The Volt doesn't go any miles on a charge yet, because it does not exist yet. What you mean to say is that GM claims it will go 40 miles on a charge, but I don't think they're even making that claim any more. Anyway, if they ever actually sell a Volt to a consumer, perhaps we'll be able to read an independent test of how far it goes.

Second, once the charge is depleted, the Volt does not operate anything at all like a Prius. See below.

Originally Posted by BoostedTimmy

... so often I see the synergy drive doing exactly this, not drawing current from the battery but the ICE powering the front wheels AND the electric motor....what is the point in this? Under hard acceleration it seems to draw from the battery so I can't see how this helps in any possible situation?

The Prius PSD (power-split device) sends 60% of the torque to the wheels, and 40% of the torque to MG1. But since force transmits power only in proportion to velocity, the Prius engine is sending most of its power to MG1 at slow speeds and most of its power to the wheels at high speeds. Power sent to MG1 can (at the discretion of the computer) be used to charge the battery or to power MG2, which powers the wheels, allowing the engine to run at high (efficient) RPM even when the car is moving slowly.

This is why under hard acceleration you will see power from the engine following two routes to the wheels, one direct, and the other via MG1.

John's web site has some excellent tutorials on how the Prius operates.

If the Volt allowed the engine to actually recharge the battery pack and then shut off, it would greatly improve its efficiency. But apparently charge-sustaining mode does not work that way, instead just using the energy from the generator to power the wheels, giving it all the losses of the dual conversion, but none of the advantages of a uniform power output from the engine.

GM has a hundred-year history of lies and deception. They have earned our distrust. I do not believe a thing they say about the Volt. They could have built and sold it years ago. We're still waiting. I won't believe any claims GM makes about the Volt until Consumer Reports tests one. And they can't test one until GM sells one. And if they ever do, I'll eat a chocolate bunny!

[hampdenwireless]

Originally Posted by daniel

The Volt doesn't go any miles on a charge yet, because it does not exist yet.

There are many pre-production Volts driving around now.

Originally Posted by daniel

If the Volt allowed the engine to actually recharge the battery pack and then shut off, it would greatly improve its efficiency. But apparently charge-sustaining mode does not work that way, instead just using the energy from the generator to power the wheels, giving it all the losses of the dual conversion, but none of the advantages of a uniform power output from the engine.

False again. We know that the battery is active in charge sustaining mode. Just due to the optimization of the gas engine to specific RPM's we get efficiency advantages.

Originally Posted by daniel

GM has a hundred-year history of lies and deception. They have earned our distrust. I do not believe a thing they say about the Volt.

And that attitude colors most of what you say about the Volt.

I think the Volt is an excellent approach to both fuel efficiency and energy independence. It is a very different approach then the Prius and I think it deserves a chance. In some ways its better, in some ways its worse. Customers will have more choices and for some the Volt will be better (or much better) then the Prius. Due to many factors the Prius will most probably be a better fit for most customers then the Volt.