calculation details of Volt's 230mpg city estimate

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.

 

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.

 

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

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

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.

 

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.

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

 

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.

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.

 

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.

 

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.

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.

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!

 

There are many pre-production Volts driving around now.

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.

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.

 

So they say. But whether they'll actually ever sell the thing is anybody's guess, and whether the production model will resemble the pre-production cars is just as uncertain.

You know? You mean you've got access to the inside engineering specs?

GM's history of lies and deception colors my attitude toward the Volt.

I agree that it deserves a chance! That's why I want GM to get off its rear end and let people buy the thing. Or are they just going to lease it, so they can call them all back and crush them like they did with the EV1?

Remember the EV1? The people who had them loved them and wanted to keep them. They offered to buy them. They offered to release GM from any liability. But GM didn't want the public to see how nice EVs are. So GM took them back and crushed them. Perfectly good cars!!! They #*&%ing crushed them!!!

So I agree with you. I want GM to give the Volt a chance! But I don't believe they will, and I repeat my statement: If GM actually markets the Volt I'll eat a chocolate bunny. I'll even post pictures.

 

But it is very similar in that similar engine management can be used to use the battery as a buffer with the engine being power controlled to provide the average power needs.

As you say the losses will be larger that in the Prius because the electrical path losses will be around 20% instead of the 5-10% in the Prius.

kevin

 

The Volt will have no where near 20% electrical losses in the electrical path. High power electronics have advanced to the point where 2% is possible, the Volt will have less then 5% electrical loss for the power going from the generator to the motor. In most cases the electronics and cooling combined for the more efficient electronics are going to cost less then having worse electronics and more cooling.

The Volt will have less electrical losses charging and discharging its batteries due to them being Li-ion batteries over NiMH.

 

I'm in no position to defend GM, that is for sure. But I can understand why charge-sustaining (CS) mode does not have a definite "mpg." ICE burn will be headed towards the battery at varying rates, at different vehicle speeds.

I agree with Daniel that consumers have to learn what Kwh/mile means. We also have to know the useful charge capacity of the car's battery. THEN the EPA can test energy consumption in EV and battery charge constant ICE modes in the different test cycles.

Timmy: the '40 miles EV range' was indeed generated on the easy, slow speed city test cycle. The same cycle that the Prius scores 60 mpg. So a person who gets around 40 mpg in their Prius city driving, is going to have about a 27 mile EV range in the as-spec'd-vapor volt.

I personally have no negative opinions against the serial hybrid design at all, though I doubt it has inherent advantages over a PHEV-HSD design in mixed use. I do think the GM Volt as outlined in the PR blurbs is a stillborn, because it was spec'd according to marketing requirements for government aid and 'greenery' rather than the realities of battery cost, and common use patterns.

 

HW,
20% conversion losses sounds like a lot to me too, but 5% ?
Aren't PHEV chargers using up 10% to send electricity from home outlet to battery ?

Anybody know what the g/m electrical loss in a series hybrid train is ?

 

They don't say. They video: (the second one is more interesting)

pre-production test ride

pre-production assembly line

That is exactly what I said! We are in agreement.

Which was stupid. To me it was criminal. They should have had to payed CARB fines equivalent as if they never had built them. Please don't forget that Honda and the others who did similar. Cheers to Toyota for not crushing ALL of their excellent electric RAV4's.

 

Well damn, I lost my post.
I'll summarize and say that a colo.edu paper estimated that 30% of energy is lost in a series hybrid when it flows from ICe -> battery -> wheels.

Here is the pdf:http://www.google.com/url?sa=t&source=web&ct=res&cd=1&url=http%3A%2F%2Fecee.colorado.edu%2F~ecen2060%2Fmaterials%2Flecture_notes%2F2060_HEV_2.pdf&ei=fH25StW4DpPqsQOH-5Ql&usg=AFQjCNFNNbrNa1_7Nq51C9Xnd8YQ0hbI_g&sig2=Q4lKwFMjylmYPIBoB2A36A

As I understand the Volt spec, steady state ICE use will bypass the battery, so the electrical losses will accrue from a single G/M transition during that mode of operation.

The final electrical losses will be a blend of these two electrical flows.

 

PHEV chargers may loose 10%..... that is not great but only increases charging cost and time 10% over a PERFECT charger. That 10% loss does not cost range.

5% from the generator to the motor is reasonable and could be even lower. It is possible in time to have a number like 1% loss in this area as high power electronics improve. These improved electronics would benefit the Prius as well.

Series drive systems are not inefficient. They are used in trains, cruise ships and even heavy equipment. There seems to be a lot of talk here that the electrical path is so much worse then the mechancial path yet this paper shows a similar loss in the Prius MECHANICAL paths:

http://www.google.com/url?sa=t&sour...verter&usg=AFQjCNF8Q0WK37YXbohfS1RIrYLHHDnpgQ

 

Showing videos of pre-production tells us nothing about what the final production model will do, or even if they will actually go ahead with production. -- Or will they build 500 of them and then claim there's no demand and kill the project? Or refuse to sell them, just lease them, build 500 or even 5,000 and then require people to fill out an application (like they did with the EV1) and reject 99 out of 100 applicants and then say there's no demand? Or will they sell the car but lease the (patented) battery so that this time they only have to recall the batteries to leave owners with a non-functioning car?

I want to see the Volt built and marketed. But GM's history of screwing the country tells me that whatever happens won't be what they're promising.