calculation details of Volt's 230mpg city estimate

[ShellyT]

50 MPG was indeed the estimate once... upon a time... when the engine was still a 1.0 liter 3-cylinder. The switch to a 1.4 liter 4-cylinder rendered the original numbers obsolete.

That seems to be the Volt's possible downfall, or at least a symptom of it. It seems to me that GM was thinking, "we've made an EV, how hard is it to put on a generator?" Once they started, they then realized it will take more time to get the control system running at point of running at optimum efficiency and reliability for the generator and battery. And then the cost of doing so became and factor, and using off the shelf parts was decided upon.

The truly daring would have went with a wankel rotorary or microturbine that was further downsized for space and weight.

[daniel]

Originally Posted by ShellyT

The truly daring would have went with a wankel rotorary or microturbine that was further downsized for space and weight.

Steam. Steam cars failed for reasons of marketing, not technology. They have the advantage that external combustion can be much cleaner. And with a PHEV, startup time is not an issue.

But of course with GM you are guaranteed to get crap, designed to screw the consumer. Reliability? Forget it! Quality? Forget it! Energy independence? No way! Not as long as GM owns a chunk of Big Oil!!!

[kevinwhite]

Originally Posted by ShellyT

...

The truly daring would have went with a wankel rotorary or microturbine that was further downsized for space and weight.

They would have been bad choices as they are so inefficient (especially the turbine).

The best choice is a reciprocating engine - sized to be able to efficiently generate the average power needed for high speed cruising. To meet this requirement you will need a 1-2 litre engine. Pretty much what they have ended up with in the Volt and the Prius.

kevin

[usbseawolf2000]

John,

Any reason why vacation miles are not consuming gasoline?

[ShellyT]

Originally Posted by kevinwhite

They would have been bad choices as they are so inefficient (especially the turbine).

The best choice is a reciprocating engine - sized to be able to efficiently generate the average power needed for high speed cruising. To meet this requirement you will need a 1-2 litre engine. Pretty much what they have ended up with in the Volt and the Prius.

kevin

In a series hybrid hybrid application, where the engine has no direct link to the drive train, you can have the engine operating at a much narrower rpm range, which makes it easier to design for efficiency. Remember, part of the Prius' success with fuel economy is downsizing the engine to the point where it spends most of time at its efficiency peak, instead of below it because the engine needed to be oversized to occasionally pass and climb hills. A series hybrid with battery can take further advantage of an engine's economic sweet spot by having it spin only at that rpm.

Ideally, a series PHEV would have a genset that had a very narrow set output. It would generate enough power for a set cruising speed. This depends on average speeds in the country of destination and amount of buffer from the battery. Likely 75mph in the US with the shorter EV range of the 1st gen vehicle. Once the charge of the battery hits a setpoint, same 50%, the genset kicks on. If you aren't going that set cruise speed, the excess power generated goes into the battery. Eventually the battery will be topped off, and the genset will shut off. Going above the set speed meanstapping into the battery. Eventually, doing so for extended periods will put the car into a turtle mode, a la the 1st gen Prius. But this is a 1st gen of our ideal series PHEV.

It doesn't sound like the Volt does this. Getting such a system right would take time to develope and research. Whatever the reason; pressed for time, greed, simply daunted, etc., GM went with an EV that happens to also be a standard series hybrid. Which means using an engine with a more variable output.

Back to our ideal S-PHEV, the reason to use a wankel or micro turbine is for weight and space savings. A reciprocating engine may have an advantage in efficiency. The narrow rpm range needed for the application should narrow that gap, but even if it doesn't, for most people the electricity for daily driving is coming from the grid. In which case, a smaller, lighter engine means more room for cabin and cargo space. Maybe a slight edge in battery range, or even more options for installing the genset.

This is going th be simplistic. The RX-8 is the only available wankel engined car. It's 1.3L gets 19mpg combined. The Yaris gets 31mpg from a 1.5L 4 cyclinder. That isn't a complete picture. The 1.5 produces 100hp. The 1.3, 230hp on premium, so lets say 200hp on regular. In a generator, the 1.5 will have to run longer to match the electricity generated by the 1.3. Which means burning about as much gas, maybe more, as the 1.3.

Efficient electric generation doen't necessarily require the same considerations as driving economy.

[john1701a]

Originally Posted by usbseawolf2000

Any reason why vacation miles are not consuming gasoline?

I was being generous... and was quite curious what the initial response would be, since this thread was being monitored by the big GM forum. So for first round, I just made a side mention.

Waiting until later, I could fill in those blanks. After all, 460 miles of continuous CS driving is quite a blow to their gas usage expectations.

It's easier to press a point when you have real-world data available... which is what I've been collecting in the meantime.

.

[JRitt]

With different modes of generating power for cars the EPA should list the cars in a cost per mile to operate @ a set cost for the unit of fuel. For example
A pure electric vehicle cost $.03/mi city and .05/mile highway @$.10/Kw*H
A pure Gas vehicle cost $.07/mi city and $.05/mi highway @$2.50/gal
or any combination of the above.
Anything else and it leaves the consumer guessing about what the most economical vehicle is for their use

[john1701a]

Originally Posted by JRitt

Anything else and it leaves the consumer guessing about what the most economical vehicle is for their use.

The purpose of this effort is reducing our dependence on oil (and the corresponding emissions), which is pretty easy to show even with just estimates.

Most economical, as opposed to "worth paying a little more for", is going to be a challenge for quite some time. We need lots of real-world data for that. Waiting for production ramp-up will help too.
.

[djasonw]

I'm a bottom line type of person. Here's my question GM. I plan on taking a 200 mile round trip to the Pocono mountains. What is my MPG ~ going to be on this trip. If you claim the car gets 240mpg that means I'll use less than a gallon of gas? DUH... of course not. U know something? GM deserves to have gone under. They're still a bunch of morons. Liars, swindlers etc. So tell me GM... what's it gonna cost me in fuel to go round trip to the Poconos from NYC. ...Pardon me??? Ok when are you going to get back to me?? Ok thanks.. thought so. IDIOTS!!

[daniel]

Originally Posted by JRitt

With different modes of generating power for cars the EPA should list the cars in a cost per mile to operate @ a set cost for the unit of fuel. For example
A pure electric vehicle cost $.03/mi city and .05/mile highway @$.10/Kw*H
A pure Gas vehicle cost $.07/mi city and $.05/mi highway @$2.50/gal
or any combination of the above.
Anything else and it leaves the consumer guessing about what the most economical vehicle is for their use

Originally Posted by djasonw

I'm a bottom line type of person. Here's my question GM. I plan on taking a 200 mile round trip to the Pocono mountains. What is my MPG ~ going to be on this trip. If you claim the car gets 240mpg that means I'll use less than a gallon of gas? DUH... of course not. U know something? GM deserves to have gone under. They're still a bunch of morons. Liars, swindlers etc. So tell me GM... what's it gonna cost me in fuel to go round trip to the Poconos from NYC. ...Pardon me??? Ok when are you going to get back to me?? Ok thanks.. thought so. IDIOTS!!

There is no way to give a cost per mile in a car like this without knowing how long the trip is, and the price today of both gas and electricity.

What we need, as I've said before, are two figures:

We need to know the watt-hours per mile, or (what amounts to the same thing) the miles per kWh, when the car is running on batteries, and

We need to know the miles per gallon when the car is burning gasoline.

Obviously a 20-mile trip will cost less per mile than a 300-mile trip. With the above two figures (but only if you know both the above figures) you can figure out the cost of a given trip based on current or projected fuel and electricity prices.

GM is being underhanded, disingenuous, and downright dishonest when it gives the 230-mpg figure without breaking down the separate electric and gas usages!!! Of course car makers never gave us FE numbers until the government forced them to, and they will not give us the numbers we need now unless they are forced to, because GM is run by criminals who will use every dishonest and underhanded means they possibly can to sell cars.

The government (in this case the EPA) needs to force them to provide separate electric and gas efficiency numbers.