: Chevy Volt Engine Won’t Recharge Batteries While Driving; Just A Regular Plug-In



scottf200
05-01-2011, 07:07 PM
This is a point I find myself making over and over to different people (test drives, etc) on one of the distinctions of the Volt over a typical hybrid! Old but a goodie.

http://jalopnik.com/#!5054642/chevy-volt-engine-wont-recharge-batteries-while-driving-just-a-regular-plug+in-hybrid

Sep 25, 2008 10:40 AM

Ben Wojdyla — Edmunds Inside Line is reporting the Chevy Volt apparently doesn't use the engine to recharge its batteries while driving, going against what every media outlet — CNBC, the buff books and every web site including this one — have reported as fact for the past two years. Confusion apparently stems from a press release issued when the concept version of the Chevy Volt was first revealed in 2007 indicating:


"When the battery is depleted, a 1-liter, three-cylinder turbocharged engine spins at a constant speed, or revolutions per minute (rpm), to create electricity and replenish the battery."

Instead, we're now being told, via the press release from last week's production reveal:


"a gasoline/E85-powered engine generator seamlessly provides electricity to power the Volt's electric drive unit while simultaneously sustaining the charge of the battery."

So, after some portion of the initial 40 miles of all-electric driving depletes the battery, the engine will be used to "sustain charge" while powering the electric drive directly — and not to charge up the battery. Perplexed by this apparent change in course, we placed a call to Chevy spokesman Terry Rhadigan to find out more — and figure out why the Volt isn't just a regular hybrid?

According to Rhadigan,


"The reason it does that is because we want you to arrive with the batteries 'empty,' filling up on grid power costs about 1/6th of what it does with gas."

In this sustaining charge mode, the Volt never actively tries to recharge the battery. Energy from regenerative braking is dumped into the battery, but at stop lights the engine will actually power down, saving gas rather than recharging the battery as we'd always thought. We incorrectly assumed, after our conversation on the Volt using GPS to determine efficient charge capacity on the battery with "Maximum" Bob Lutz at the production Volt reveal, it would do just that.

So basically, the Volt's not a hybrid because it still only has one drivetrain, an electric one. The engine makes electricity to power the electric motor running the wheels as well as to "sustain" the batteries, but not to charge them up. It's still, we guess, an Range-Extended Electric Vehicle (REEV), as GM's always claimed.

We don't know how to feel about this news. Certainly, from an engineering perspective and total cost of operation, it does make sense. That 1.4-liter four-banger doesn't have the power to both motivate the quite-beefy Volt and recharge the battery pack, and it probably allows the on-board generator to take advantage of constant RPM efficiency tricks. But, it again tells us we must keep our guard up on the marketing spin here. There's no doubt the Volt has changed the way hybrids are developed already, but it may also change the ways they're sold to the public. [Edmunds Inside Line]

Rusty
05-01-2011, 07:29 PM
This is a point I find myself making over and over to different people (test drives, etc) on one of the distinctions of the Volt over a typical hybrid!

And if you've ever gotten the "Propulsion Power Is Reduced" message just before you get to that lovely mountain meadow, you know very well that there are times the engine runs to charge up the battery. And it runs very hard, thank you. It just doesn't run (much?) past what it needs to get to normal CS SOC.

In a typical hybrid (including the PiP, I believe) the only way to get energy into the batteries while driving is regen.

Marc Lee
05-01-2011, 09:09 PM
So basically, the Volt's not a hybrid because it still only has one drivetrain, an electric one. The engine makes electricity to power the electric motor running the wheels as well as to "sustain" the batteries, but not to charge them up. It's still, we guess, an Range-Extended Electric Vehicle (REEV), as GM's always claimed.

We don't know how to feel about this news. Certainly, from an engineering perspective and total cost of operation, it does make sense. That 1.4-liter four-banger doesn't have the power to both motivate the quite-beefy Volt and recharge the battery pack, and it probably allows the on-board generator to take advantage of constant RPM efficiency tricks. But, it again tells us we must keep our guard up on the marketing spin here. There's no doubt the Volt has changed the way hybrids are developed already, but it may also change the ways they're sold to the public. [Edmunds Inside Line]

" the Volt's not a hybrid.." well GM did subsequently reveal that under certain high speed high demand conditions it was more efficient to just throw mechanical energy from the ICE to the wheels, so there are so circumstances where it is "sort of" like a hybrid, but certainly the vast majority of the time it is more like an EV.

"We don't know how to feel about this news." Edmunds, Edmunds, Edmunds. When I reflect on their reporting about the Volt, I imagine what an "Edmund's" report about the Wright Brothers first flight would have sounded like. Rather like this I should imagine:

The aircraft was of flimsy construction. And certainly the controls are way too difficult for anyone to acutally use. It is more likely that people will be killed by this craft than actually benefit from any sort of air travel. It is a wonderful thought that man might actually fly through the air like a bird, but this overpriced plane proves that travel by horseless carriage is the rightful place of people.

But seriously the not knowing how to feel about the news that the Volt doesn't actually try to fully recharge the batteries? I guess it was early in the game but still one would think that those in the auto journalism industry would understand the concept that an EREV does not want to fully recharge the battery, but rather sustain a minimum level so that the recharge can be done using more economical grid power than an ICE. Um...hello?

I don't know how to feel about the fact that my air conditioner turns itself off all the time, and then later comes back on. On and off, on and off. Seems like some sort marketing gimmick to me. I'm on to you Carrier!

PatsVolt
05-02-2011, 09:40 AM
Edmunds would have said that it was not a true heavier then air aircraft, because the early versions were launched off a catapult using a slide rail and a tower with a weight that dropped to launch the aircraft. They would note that the Wright plane could not launch itself without the catapult.

Pat

bonaire
05-02-2011, 07:00 PM
Edmunds better not review babies... If they did:

"These small versions of actual human beings do not seem to be as-good as or capable-of full size humans. They talk in an almost unintelligible manner. It may not even be talk but rather some nonsensical babo-speak. Their legs do not allow them to walk in an upright manner so their motor-skills seem lacking and unfulfilled. Generally speaking, these mini-humans or 'babies' do not appear worthy of mention in their current model year. Poor engineering seems to be their undoing with constant leaks, blow-outs and other forms of liquid expulsion. Edmunds believes there is no market for such sub-humans and generally feels that they have a niche market which cannot be explored as viable."

Frank F
05-02-2011, 08:37 PM
bonaire -

That one made me laugh out loud and almost spill my coffee! Leaks and blowouts indeed! Good one!

HOUSTONVOLTAGE
05-03-2011, 12:38 AM
I've had my Volt a little over a week, and I am constantly amazed at the need to explain to EVERYONE that the car is not stuck if it runs out of battery power. I'm no longer shocked by people misunderstanding how the Volt works, and I have a MUCH greater appreciation of the task GM has ahead of it in educating the market as to what exactly they are offering. I am doing all in my power to help, but its really a bigger problem than I ever knew! My suggestion for GM marketing - show the Volt running out of battery power - the passenger scared to death - the driver smiling - and the instrument cluster flashing the battery going away and the fuel tank coming into view. Ok, I'll keep my day job, but I think it would be a great commercial!

Chevrolet Customer Svc
05-03-2011, 10:57 AM
Thanks for the suggestion HOUSTONVOLTAGE! It is hard to believe that there is still such a misunderstanding about the Volt. The Volt is an innovative, never-been-done-before car that exists alone, in a brand-new category of cars. However, under the strict interpretation of the SAE definitions, it is true that the Volt would qualify as a hybrid, since it has multiple power sources on board. The ability to provide unlimited range when in extended-range operation is what makes the Volt unique and is why we like to call it an electric vehicle with extended range. In the end, we have delivered a solution that enables customers to drive gas-free, with the flexibility of having one of the most efficient vehicles even in extended-range mode.

Volt Advisor Trevor
Chevrolet Volt Advisor Team

bonaire
05-03-2011, 09:40 PM
In some ways, I would think that in 10 years, the term "Volt" will be a memory. The name Volt refers to the electrical usage of the car but the design is more than that. It is somewhat game-changing and unique to have an electric car with on-board charge sustaining technology (not just re-charging). The car's named Volt today but in 10 years when such a car is more commonplace and in-demand, you can hide the technology in other Voltec type vehicles.

Maybe a Camaro (e) - with "Electro-Gen" drive technology (Electric motor + Generator) or something like that. The whole Volt "electric car" is still hard for some car magazines to even understand let alone an average Joe or Jill.

Plug in cars with on-board generation is the right way to go. EV alone isn't going be as useful to most peopl as the Voltec.

And definitely push for use of non-rare earth electric motor technologies. We don't want the advent of the EREV to be girdled by China who has cornered the market on delivery of those resources.

It'll be a long while before electric motor cars will be commonplace but it's nice to watch the roll-out.

Slapshot28
05-04-2011, 01:31 AM
Lately I've found a quick way to summarize EV's vs Hybrids vs Conventional cars:

1. Conventional: no battery, big engine
2. Hybrid: small battery, big engine
3. Volt: big battery, small engine
4. Pure EV: big battery, no engine

Everyone seems to agree that #1 soon will be a dying breed. They also seem to think that #3 makes the most sense (even though many of them drive #2 currently). Option #4 is kind of special purpose, commuter-only car.

OMG, I see a 2 x 2 matrix here. (Now I'm terrified...) Note that the hybrid is closer to conventional, and the Volt is closer to Pure EV.

scottf200
05-04-2011, 01:47 AM
Lately I've found a quick way to summarize EV's vs Hybrids vs Conventional cars:
1. Conventional: no battery, big engine
2. Hybrid: small battery, big engine
3. Volt: big battery, small engine
4. Pure EV: big battery, no engine


I would think this would be more like 3.

3. Volt: medium battery, small engine

'big batteries' are 100+ mile PR ratings (Leaf, Focus, Tesla)

'medium battery' lets you charge on 110/120v overnight easily. 40 miles came from studies. See: http://gm-volt.com/2007/12/06/how-did-gm-determine-that-78-of-commuters-drive-less-than-40-miles-per-day/

Rusty
05-04-2011, 02:58 AM
1. Conventional: no battery, big engine
2. Hybrid: small battery, big engine
3. Volt: big battery, small engine
4. Pure EV: big battery, no engine

I'd replace "battery" with "motor". It could be argued the PiP has a big battery (well, it could!). But it's still a small motor/big engine car. It's really what's instantaneously providing power to the wheels that matters, not how long it can do it. A 13 mile range big motor/small engine car (aka Voltec puny) would be very different that a 13 mile range small motor/big engine car (aka PiP).

After deciding the drive train, it's just an argument about how long a type 3 can move on the battery.

JohnK
05-04-2011, 09:46 AM
Thanks for the suggestion HOUSTONVOLTAGE! It is hard to believe that there is still such a misunderstanding about the Volt. The Volt is an innovative, never-been-done-before car that exists alone, in a brand-new category of cars. In the end, we have delivered a solution that enables customers to drive gas-free, with the flexibility of having one of the most efficient vehicles even in extended-range mode.

Volt Advisor Trevor
Chevrolet Volt Advisor Team
Not only that, but I have a devil of a time explaining how the "300 mile range" of the Volt does not compare in any way at all to a 300 mile range EV (like a Tesla Model S), because it only takes 5 minutes to "recharge" the gas tank. I am NOT limited to 300 miles, but can easily go 1200 miles with just potty and gas stops.

Xzlon
05-13-2011, 11:12 AM
You can force the ICE to charge the battery by driving alternately between Mountain Mode and Normal. Just switch to MM when the CD mode gets near to zero miles left then switch back to Normal after the ICE has charged the battery for a while. Then repeat. It would not be too good for your overall efficiency in flat land driving a but I do this on uphill grades to combine drive power and battery charging when I know that later I will be running in CS mode anyway. I then drive my last few miles of my trip in Normal/CS to deplete the last of the battery charge before I get home. Doing this I get more recorded CD miles on a trip. Of course the battery is not charged fully in MM, but charge is added by the amount of reserve that is programmed in for MM.

DonC
05-13-2011, 03:30 PM
I've found that "electrical power station" is a key descriptor. I used to say motor-generator and that just confused people. Now I say the Volt is an electric car. It uses a battery but when that runs out it has it's own electrical power station that generates electricity. If someone asks how the power station works I just say it's a generator like you might use for your house in an emergency.

Seems to work better than anything else. YMMV.

saghost
05-17-2011, 04:28 PM
I'm new here, but I've been lurking a while. A Volt might be my next car (though I'd have a hard time giving up my convertible.) This post convinced me to register, since it's something I've wondered about on occasion (wasn't expecting it to take 4 days.) Disclaimer: I am an engineer, and sometimes it shows... :D


You can force the ICE to charge the battery by driving alternately between Mountain Mode and Normal. Just switch to MM when the CD mode gets near to zero miles left then switch back to Normal after the ICE has charged the battery for a while. Then repeat. It would not be too good for your overall efficiency in flat land driving a but I do this on uphill grades to combine drive power and battery charging when I know that later I will be running in CS mode anyway.

The Prius has a hypermiling technique they call "pulse and glide," or PnG, which involves accelerating fairly hard up to a given speed, then drifting engine off down 5-10 MPH and repeating. It works because internal combustion engines are generally more efficient at higher power settings - typically they are most efficient at 90+% throttle near the "peak torque" RPMs.

With that in mind, I wonder if cycling mountain mode might yield something similar - put the car in mountain mode until the engine slows down, then back to normal until it kicks on again and repeat. If the gain in efficiency in the engine is greater than the losses in the generator and battery, it should result in better economy.

If someone's bored on a long road trip, I'd be interested to see how it works in practice. You'd have to be careful how you calculated it, because the car would register some of your "gas" miles as electric miles.
Walter.

voltage692
05-18-2011, 12:24 AM
Could there be a more annoying way to drive? I hope Prius people don't make a habit of this technique.


I'm new here, but I've been lurking a while. A Volt might be my next car (though I'd have a hard time giving up my convertible.) This post convinced me to register, since it's something I've wondered about on occasion (wasn't expecting it to take 4 days.) Disclaimer: I am an engineer, and sometimes it shows... :D



The Prius has a hypermiling technique they call "pulse and glide," or PnG, which involves accelerating fairly hard up to a given speed, then drifting engine off down 5-10 MPH and repeating. It works because internal combustion engines are generally more efficient at higher power settings - typically they are most efficient at 90+% throttle near the "peak torque" RPMs.

With that in mind, I wonder if cycling mountain mode might yield something similar - put the car in mountain mode until the engine slows down, then back to normal until it kicks on again and repeat. If the gain in efficiency in the engine is greater than the losses in the generator and battery, it should result in better economy.

If someone's bored on a long road trip, I'd be interested to see how it works in practice. You'd have to be careful how you calculated it, because the car would register some of your "gas" miles as electric miles.
Walter.

Rusty
05-18-2011, 12:31 AM
Could there be a more annoying way to drive? I hope Prius people don't make a habit of this technique.

You don't live in California, do you?

saghost
05-20-2011, 04:41 PM
Could there be a more annoying way to drive? I hope Prius people don't make a habit of this technique.

It's extremely annoying, the couple times I've come across it - especially since I prefer to use cruise control a lot on longer trips.

My point, however, was that I think something similar could be achieved at a steady speed by the intermittent use of mountain mode on a Volt.
Walter

mfennell
05-20-2011, 05:15 PM
Around town, the Volt essentially does this already, except it's controlled by the ECU that understands all the current parameters, backed up by considerable testing and data logging. They (GM engineer) have juggled optimum mileage, emissions requirements, and (unfortunately for ultimate economy!) NVH considerations. I don't see how we can beat that by gaming mountain mode, especially since after switching into mountain mode, the car will be on a mission to restore SOC to 45% or so, rather than necessarily operating at its most efficient point, plus you're increasing the percentage of power that has to go into and back out of the battery.

If you ever hook up a scanner, you'll see that, at least at lower speeds when it's running serially, the ICE is running nearly WOT, maximizing efficiency at whatever rpm it's maintaining. You might think that ideally, it would match power output to the electric motor precisely (minimizing losses into-out-of the battery) but that is not practical and apparently not necessarily the most efficient way to do it.


I have always had trouble understanding how the Prius approach works. Is accelerating/decelerating between 55 and 65 (or whatever) really more efficient than just driving the same average speed, which would be something less than 60 in that example? OK, you get some reduced pumping losses with the throttle open more as you accelerate, sure, but running 90+% throttle, you run the risk of throwing it all away by running into enrichment mode in the fuel map. Also, the power you use to moderate your coast down came from gasoline originally, only now it's going through more conversions.

I know people are super into this but I've always wondered if anyone has done a controlled test. Acceleration is not free, nor is the restart every time you "pulse".

saghost
05-20-2011, 06:13 PM
I have always had trouble understanding how the Prius approach works. Is accelerating/decelerating between 55 and 65 (or whatever) really more efficient than just driving the same average speed, which would be something less than 60 in that example? OK, you get some reduced pumping losses with the throttle open more as you accelerate, sure, but running 90+% throttle, you run the risk of throwing it all away by running into enrichment mode in the fuel map. Also, the power you use to moderate your coast down came from gasoline originally, only now it's going through more conversions.


In terms of energy the car needs, no, constantly shifting between 55 and 65 isn't more efficient than driving at 60. It requires more total energy (kwh) to do (not a lot more, but because drag is a function of velocity squared, the 65 piece takes more extra energy than the 55 piece saves, if that makes sense - the difference is pretty trivial, and not the point of the exercise anyway. The energy put into acceleration you get back in the deceleration.)

However, the engine is more efficient doing it, which can make the entire operation more efficient. A web search says this is a bsfc chart for a Prius of some generation - no matter what, it should suffice to explain the idea in principle:

http://www.techno-fandom.org/~hobbit/cars/SAE-bsfc.gif

The left side is engine torque, in Nm. The bottom is engine speed in RPM The contour lines on the chart are specific fuel consumption, most likely in grams/kwh - how much fuel it takes to generate one unit of power.

To extend the example we've been talking about, say that the car requires 15 kW to sustain 60 MPH on flat land (probably in the right ballpark, but a complete SWAG.)

Driving normally, you need the engine to produce that much the whole time. If the chart is right, the Prius will choose to do this at 1900 RPM at 75 Nm or so, yielding around 240 g/kwh. (already quite efficient.)

With pulse and glide, you'd attempt to use the most efficient part of the bsfc map - around 3k-3500 rpm at 95 Nm for almost 30 kW, netting somewhere slightly below 230 g/kwh. (because of the details of the engine design, the engine uses less than 96% of the fuel to achieve the same amount of energy - the engine is better at converting fuel into power at that speed.)

So you need less than 1% more energy to move the car (average of squares of 55 and 65 is 3625, .7% more than 60 squared, and overstates the difference,) but you get over 4% more energy from the same fuel. To my mind, not worth the trouble, but a real savings nonetheless. (Most cars aren't operating nearly as efficiently, but to get the gains shown you'd have to shut the engine down completely, like the Prius or the Volt does.)

Make sense now?

I haven't seen a Volt bsfc chart, so I have no idea how much more efficient it is in the higher power speeds than the lower power ones. You'd need enough efficiency gain to offset the charging losses in the battery for it to work out.
Walter

marlow
05-21-2011, 10:56 AM
I do not think that the Prius Pulse driving is going to help with the Volt at all. Sense in the Volt the computers are all ready usng the ICE to maximum efficency for the current situation, sort of automatic pulsing (while in CS mode) while still allowing you to go what ever speed you want to.

Remember, in the Prius the "gas" pedel is in control of the ICE, it is not in the Volt, the computers are.

As far as intermittently using mountian mode as a different form of pulsing, I have tried that and the energy conversion losses exceed the efficency gains.

I think that on a long trip, using Mountian Mode to reserve some battery power for slow speeds and stop and go driving conditions is more efficient.

The most efficent why to drive a Volt is at a constant speed of around 45 MPH, with concideration of weather, road conditions and climate settings.

If road conditions are good but the outside temp is very high or low a faster speed may be better (assuming the windows are closed) as that would mean the climate controls would not have to run for as much time.

In a heavy rain, a slower speed will be more efficient.

Sharkonwheels
03-09-2012, 11:31 PM
Digging up an old thread...

Wondering... Can someone explain why the decision was made to not charge the battery?
Here's my take:

If you've depleted the battery, and the ICE start up, and is burning fuel and spinning the generator to create electricity, why wouldn't you funnel the extra to the battery? For example, in my 2009 Cobalt SS, I have the RPD display, which shows me HP and Torque the engine puts out. To cruise @ 70, the car claims 30-35HP. 30hp converts to 22kW, 35hp converts to 25kW. If it's a 55kW generator, why not send extra to the battery? You're already burning fuel, might as well get the max efficiency out of it while you're burning it.

Or am I missing something?

saghost
03-10-2012, 01:58 PM
Digging up an old thread...

Wondering... Can someone explain why the decision was made to not charge the battery?
Here's my take:

If you've depleted the battery, and the ICE start up, and is burning fuel and spinning the generator to create electricity, why wouldn't you funnel the extra to the battery? For example, in my 2009 Cobalt SS, I have the RPD display, which shows me HP and Torque the engine puts out. To cruise @ 70, the car claims 30-35HP. 30hp converts to 22kW, 35hp converts to 25kW. If it's a 55kW generator, why not send extra to the battery? You're already burning fuel, might as well get the max efficiency out of it while you're burning it.

Or am I missing something?

It's not that simple, but the Volt does charge the battery in certain circumstances. In the big picture, the reason it doesn't charge the battery is that wall power is typically about a third the price of gasoline on a mile by mile basis, without counting time of use or other discounts.

In the small picture, every engine has a speed and throttle setting at which it is most efficient. Typically, this is near the torque peak at just below full throttle, though it can vary with some engines. So running the engine at peak rpm at WOT will produce less power per unit of fuel consumed, in addition to being really noisy.

When the car's power needs get low enough that the engine running at WOT at 1400 RPMs is making too much power (typically around 60 on the open road,) the Volt starts charging the battery instead - it goes to 'virtual 6th gear', stopping MG B and driving the car directly with the engine at around 3.1:1, while pulling excess power on MG A and stashing it in the battery. When it has ~400 Wh, or the next time the throttle lifts, it turns off the engine and runs electrically for a mile or two (or to the next throttle drop.)

tboult
03-10-2012, 02:42 PM
Walter covered the basics.

But there are time when a few of us have found that Mountain mode, which can recharge while driving, can actually improve overall milage. See http://gm-volt.com/forum/showthread.php?11118-MM-Gaming-25-gains-in-MPG-and-EV-Range!-My-experiment-results.../page2&highlight=Mountain+Mode (there are many other threads too but Joule Theif did a good detailed set of experiments)


But most usage of MMode will burn more gas than it saves. That being said, if you want to show off the car in EV mode and have depleted the battery you can just drive a while in mountain mode and it will recharge to give you 14miles of EV range. (Note if you are in CS mode it will nto show the battery icon after MM recharging unless you stop and restart).
But in general there is just not enough "extra efficiency" with the current engine.