Chevy Volt - How's it work?

[BobM3]

Chevy says it can go about 40 miles on batteries alone but can go another 200 or so miles using a small IC engine that recharges the batteries. So, in effect, the "small" IC engine is moving the car. I'm assuming that performance (acceleration and top speed) are drastically reduced when running on the engine. Or am I missing something?

 

[SomptingGuy]

Why would the performance be compromised?

This is just a series hybrid with a big battery. It seems that GM are trying to convince the journalists and prospective customers otherwise. They don't use the word hybrid and refer to the engine as a "range extender".

From what I've read, they're trying to claim that the fuel economy should be measured in such a way that it ignores the fuel used to charge the battery when it's plugged in overnight. EPA tests usually require the battery to be in the same state of charge at each end of the test (i.e. sensible).

Letting the battery discharge during the conomy test is exactly the same as starting your economy test at the top of a hill.

This car could be another "breakthrough in marketing".

- Steve

 

[ivymike]

should perhaps have two separate figures on the sticker - the gallons used per hundred miles, and the externally-supplied kWh to return to the same charge state at the end. Would take years for people to get their heads around the total cost to go 100mi. Pure marketing brilliance.

 

[bvanhiel]

It's a bit different in that the battery is large enough that most daily trips will never tap the fuel. Putting an IC engine into is the comprimise they had to make to give the car the kind of range that American's expect. Many people currently are modifying their Prius's to perform similarly.

And by the way... prior to 2008 (and maybe even now?) the EPA did not require that a hybrid's battery be in the same state as at the beginning of the test.

A plug in hybrid is a bit of a different animal than a car that gets all of it's energy from gas. It's an issue because it is illegal for the automakers to advertise any mpg except the EPA's test.

-b

 

[Bribyk]

"Breakthrough in marketing"...I like it.

 

[BobM3]

- so the car continues to draw energy from the batteries even when the battery voltage is low enough to kick on the IC engine? The Tesla supposedly will go nearly 250 miles without the IC engine and it will recharge overnite. It doesn't seem like the IC engine does much - gets you an extra 50 miles or so over the Tesla?

 

[TVP]

Bob,

I am not very familiar with the Tesla, but will it seat 4 passengers, obtain 4-5 star crash ratings, etc.? My guess is that it is more of a performance car, thus it weighs considerably less, and will have a retail cost significantly higher than that of the Chevy Volt.

 

[BrianPetersen]

The car continues drawing energy from the batteries even when the "state of charge" is low enough to start the IC engine ... YES ... but remember, the system is (apparently) designed to keep it above (approximately) 30% charged, so there will not be a loss of performance.

The "range" on a long trip that uses up the designed 70% charge, is no different from a gasoline vehicle and you treat it the same way. When the gas gauge goes to empty, you fill it up and keep going, obviously on gasoline power (driving the generator which maintains the state of charge at about 30%).

The Volt is *designed* to be plugged in every night to recharge it. It is an electric car with a range-extending gasoline engine so that it can do long trips. If you don't plug it in, you lose the benefit of running on stored electric power, but at least the car will DO it.

 

[BobM3]

I think I get it - the car runs on batteries until the battery charge gets to about 70%. At that point you run on gas + battery. When the battery is down to about 30% you are "out of fuel" and you need to recharge the batteries.

 

[BrianPetersen]

No, not quite ...

The car runs on batteries alone, without gasoline engine operation at all, until the state of charge reaches about 30%. At that point, the car continues running on batteries but the engine starts and recharges them at the same time, so the car keeps going (on "net" gasoline power) and the state of charge is kept at about 30% by running the engine to roughly match power demand. It will go as long as the tank of fuel will last in this mode just like a regular car, and you can fill up the tank and keep right on going, just like a regular car. When the opportunity arises to plug the car in ... the batteries charge to 100% and this process can be repeated. From the point of view of "running out of fuel" there is not ever a "need" to plug in the battery ... but if you don't, you will not get the fuel saving benefit of the plug-in hybrid system.

 

[SomptingGuy]

"fuel saving"?

It's only really tax saving. Fuel is burned elsewhere, with much less tax than anything you can buy at a pump.

And we all know that when tax-saving schemes become popular, they disappear.

- Steve

 

[duck0601]

It's gasoline (petrol) saving. I have seen the results of studies(propoganda?)that indicate that 40 miles would cover 80% of US driving needs.

 

[SomptingGuy]

You guys just don't seem to get it. Maybe it really is a breakthrough in marketing.

They may not be burning gasoline at the power station, but it's more than likely some form of hydrocarbon fuel that's being used to "fill" the battery.


- Steve

 

[bvanhiel]

We understand you Somptingguy, but the taxes are much different on this side of the pond. Our fuel taxes in the US are much lower on gas/petrol (10-20%) vs. what you pay in the UK (closer to 120%). We also generate a larger share (but still small) of our energy from hydroelectric plants. It's also much harder to shovel coal into your car while driving than to rely on the battery.

-b

 

[BobM3]

Brian:

When you get down to that 30% level then all the car's power needs are coming from the gas, right? That's where I don't understand how you can get by with what is called a "small" IC engine. Performance of the car must be limited at that point, right? Or is it that the electric drive is more efficient at getting power to the wheels?

 

[bvanhiel]

The small engine runs even when you're not demanding power. By running continuously it can keep the battery charged enough that it can deal with short high demand periods (accelerating from a stop). Obviously if you're towing a boat up a mountain at 80mph you'll probably overwhelm the little IC motor.

 

[BrianPetersen]

Regarding the fuel being burned elsewhere, it's true, but an electric powertrain is more efficient at light power demand and at regenerative braking, AND the central power plant has a higher thermal efficiency than a mobile gasoline engine ever could be, so the net amount of energy input is less. And that's assuming that all the electrical power is generated using fossil fuel. In the USA, that might be substantially true (for now), but there are more options for generating electricity renewably (wind, solar, hydroelectric, etc) or at least via non-fossil-fuel-consuming methods (nuclear).

Here in Canada, a very large fraction of the electricity is hydroelectric or nuclear. Wind power is still a small fraction but gaining fast.

The taxation point is a good one, and if plug-in vehicles become popular, I wonder how long it would take the authorities to do something about this.

 

[GregLocock]

Well, yes and no. By the time you've distributed the electricity, put it through the charger, and then through the car's own electronics, you are looking at something like 80% distribution (power station output to input to battery) efficiency at best. In terms of CO2 emissions there is surpisingly little difference between an EV such as the Tesla, and an efficient diesel with 4, rather than 2, seats. The Volt actually uses about 50% more power than the Tesla in EV mode.





Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[rmw]

Having just suffered through 2 weeks without power and having a generator in my driveway due to Hurricane Ike, I have wondered how if I were to have had a Volt I would have worked that into my electrical scheme. Would a 6 Kw generator that already had some dedicated loads, fridge, freezer, a few fans, lights, laptops, etc have had enough spare capacity to also charge a car that I needed for gasoline runs for gasoline that I needed in order to run the generator plus getting to work the past week? Would the device for charging the car work with a generator?

All in all, it has given me some pause regarding a plug in car. I had more devices to plug in than I had generator capacity to accommodate.

rmw

 

[GregLocock]

Well, you'd just drive around in battery depleted mode. That isn't ideal, effciency wise, since you are lugging a dead battery around, but it would work. And to be honest it only takes 16 kWh to charge it, so a 6 kW genny should handle that.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.