230 mpg in the Volt? Chevy fudging the numbers?

[Spac3dog]

Originally Posted by NeilBlanchard

So this yields ~83.5MPGe for the first 40 miles on the Volt, and then ~50mpg after that. Instead of 230mpg on the same 50 mile trip, the Volt gets 73.6mpg -- which is completely plausible and believable... why didn't GM choose this method? Sheesh.

Because 73.6mpg does not sound nearly as good as 230 does when it comes to marketing so instead they went with the huge hype number that will cause a huge backlash for them when/if the Volt actually does come out. Sounds like about par for the course for GM to me.

[MetroMPG]

I've read that GM has had some influence with the EPA in designing the formula that will be used to rate plug-in hybrids' MPG. It's unlikely they're "fudging the results" as much as they've pushed for a formula that yields silly eye-popping numbers like this.

I agree the best approach would be a dual rating: city/hwy distance on battery power alone (plus Watt hours/mile - the car's best economy measure for electric operation) ; and city/hwy MPG with the battery depleted and generator running.

The GM marketing gurus decided that the impact of any "backlash" they'll undoubtedly face from consumers who can't get anywhere near 230 mpg in their use of the car will be much smaller than the avalanche of free marketing they're currently enjoying right now from the 230 mpg announcement.

Since the vast majority of non-"car people" will only read the headlines and don't delve into the details... it's "MISSION ACCOMPLISHED" as far as the marketers are concerned.

[pgfpro]

It looks like GM is very desperate and doing what ever they can to save themselves. What a shame.

[jamesqf]

Originally Posted by NeilBlanchard

The Volt is what is called a serial hybrid (though the folks at GM want to call it an "extended range EV"). This means the electric motor pushes the car by it self, and the ICE is used to charge the battery -- this is similar to how electric/diesel trains work.

Not quite the way it works, at least from descriptions I've read. (And from basic engineering, not the way it should work for best results.) The engine/generator drives the electric motor directly (as in a diesel-electric locomotive). If the engine produces more power than needed, then the extra can recharge the battery (as can energy from regenerative braking).

The point is that there are losses in the battery charging process, so for best efficiency you don't want your gasoline engine to recharge it unnecessarily. So if you are planning a trip beyond what can be done on the battery alone, you wouldn't want to run the battery down, then switch to the gas engine. Instead, the engine should come on when the battery is partly drained, and provide a constant power output, with the remaining battery in reserve for acceleration or hill climbing.

[Christ]

Well, the 230 MPG mark is potentially true for the 51.1 mile drive cycle, but the further you go before recharging, the less your average miles per gallon becomes.

[MetroMPG]

Exactly.

What happens when you drive 230 miles in a Volt? You use way more than 1 gallon of gas.

[dcb]

I really think there should be a law where folks making these claims have to eat their own dogfood , i.e.

Originally Posted by Frank Lee

...put doofus out in the middle of the Arizona desert with his Mustang and 1 gallon of fuel and see how he likes it.

[Christ]

Originally Posted by MetroMPG

Exactly.

What happens when you drive 230 miles in a Volt? You use way more than 1 gallon of gas.

I think this quote from a GM forum (that I stole from a Tacoma forum) sums it up nicely:

Originally Posted by CustomTacos.com forum - Volt MPG thread

GM says that the Volt will go 40 miles without using gasoline. The quote from CNN tells the story better I think.

"So let's say the car is driven 50 miles in a day. For the first 40 miles, no gas is used and during the last 10 miles, 0.2 gallons are used. That's the equivalent of 250 miles per gallon. But, if the driver continues on to 80 miles, total fuel economy would drop to about 100 mpg. And if the driver goes 300 miles, the fuel economy would be just 62.5 mpg."

For the average consumer, the 230MPG thing is true, though. Most trips are under 50 miles round, right?

I still wouldn't mind going 300 miles at 62.5 MPG, though. I wonder if there is a good way to P&G with it or drive it more efficiently...

Also - I've been hearing tell that the engine will not charge the batteries at all. If this is true, I believe this is a waste of quite alot of power, considering that (as I understand it) the engine runs in steady state operation at either peak output or peak efficiency (or somewhere in between), turning a generator. Obviously, it's directly driving the e-motor here, but what happens when you don't need the available 88HP (~70 counting losses)? The rest of that available power is just "gone"? I don't see this being a truly efficient use of available energy, although I can understand the cycling effect that the gas engine would have on the batteries.

[Christ]

I also tend to wonder how large the fuel tank will be... how much of that gas gets wasted from not being used before it stales?

[mcmahon.craig]

Originally Posted by dcb

The engine should not charge the battery, at least not very much, that is what the house plug is for. and would be a waste of gas to do so.

I disagree. In the not-yet-a-series-hybrid project we have been working on for some time (a Porsche 914) we figure the opposite is true.

What we know is that the car requires approximately 10kW (about 75A @ 144V) to cruise on the highway as an EV. Far less than 53kW eh? The battery dissipates a little energy but gives you load levelling during passing and acceleration.

The general upshot of this is that we can use a naturally aspirated 125cc motorcycle engine (currently thinking Honda CBR125R - a 90MPG bike) instead of a 1.4L turbo four, since we basically only need to cover AVERAGE power (~10kW) instead of PEAK power (144kW).

Now, our battery is a lot smaller than the Volt's but taking the battery out of circuit in your "EV" doesn't make much sense.