Chevy Volt - Electric Car

[Sxotty]

Yeah the Prius is a good car for high mileage, but it gets a bit too much attention IMO in comparison to diesels which can match it in mileage. Toyota has done an amazing job cementing the prius as the green car. The best part of a prius is it is a vehicle with a large functional interior that gets great mileage.

I am extremely curious how the volt will do mainly b/c I like the series hybrid concept way more than the parallel concept as seen in almost all other hybrids (whether synergy or two mode). The series system always seemed much more elegant, but it is likely less efficient.

 

[Silent_Buddha]

Well, I wouldn't be surprised at the 100 mpg figure after all, there's a few different factors at play.

The gasoline engine is only used to charge the battery and not to directly drive the wheels. Thus there is no need for constantly changing RPMs to do adjust to changing linear velocity. So the engine can be set to always run at it's most optimum RPMs. Driving an alternator also doesn't require as much horse power or torque as driving a car.

Additionally once you go into dead battery (30% charge I believe) zone, then the cars top speed and acceleration are greatly reduced (last figures I saw were in the 50% or less range) to the point that the charging system can keep the battery at equilibrium. IE - you aren't going to get anywhere fast, but you'll still be able to get there. Lower sustained speeds and lower acceleration will both reduce the power drain on the electric motor.

It's a nice solution, but still impractical for the majory of consumers. Considering it's currently projected to cost more than 40,000 USD.

Regards,
SB

 

[Dave Baumann]

Aren't there large rebates for these though? I thought both US and Canadian governments are offering something in the order of $10K tax rebates on them.

 

[Sxotty]

SB it is possible top speed is reduced, but there is no way they are reduced to 50% or less. It has a 4 cylinder engine it will still drive.

And the vehicle will still accelerate. It will just pull from battery + engine. Wherever you read the >50% reduction thing it is very unlikely unless they screwed up royally. There is tons of FUD about the volt and stuff written by those that just don't even understand the difference between a parallel, serial hybrid, or what the EREV designation meant.

 

[Silent_Buddha]

The gasoline engine is ONLY there to charge the battery, nothing else. The charge it will provide won't allow for quick acceleration or high top speeds.

Addtionally the Volt is designed such that it will do everything it can to maintian a battery charge between 30%-80% to prolong the life of the battery. Once it hits 30% it kicks in the engine, and basically run only on the electricity generated from that.

Dave...

Yeah, in the US at least there's a 7500 USD government rebate. Processing of which is expected to take 6-12 weeks. So you still have to pay full price, but you can then ask the government for the rebate.

Current estimates is that even with the rebates, it'll be approximately 35,000 USD. However, you'll have to pay about 42,500 USD to actually get the car.

When it was rumored to be in the "high 20k USD" range, it was an intriguing option.

It's by far the best "electric" vehicle proposal, but living out in a relatively rural area, some of us have commutes of greater than 50 miles a day. I'm still betting on hydrogen fuel cels with direct drive systems.

That's another nice thing with the Volt, you can (presumably) drop in any replacement fuel based engine to charge the engine. And I wouldn't be surprised if there were eventually aftermarket modifications that put in a more gas guzzling engine charging system in order to maintain speed and acceleration.

But then that partially negates the fuel efficiency when you get into the dead zone.

Regards,
SB

 

[_xxx_]

Yeah the Prius is a good car for high mileage, but it gets a bit too much attention IMO in comparison to diesels which can match it in mileage.

The problem over there in the US is that the quality of diesel varies severely, so we always have to develop for "worst case", which makes the cars more expensive and thus less viable. And a diesel car is still somewhat "dirtier" than the Prius etc. although it'll usually rape the Prius mileage-wise.

Back to Volt: I thought it was supposed to be purely electric, with only the european version having the additional combustion engine?

BTW they had a little 3-cyl turbo in the drawer, their european daughter Opel has quite a few potent little engines, including a 3-cyl turbo in their Corsa models. Those are actually licensed from Fiat/Alfa, who develop them.

 

[Pete]

SB, I guess the 50% figure is based on how much faster the battery can discharge to the electric motor than the ICE can recharge the battery? Surely GM will try to make performance degrade/transition gracefully from all-battery to all-ICE. (Edit: I'm too slow. Your last post answers this.)

Sxotty, how do you find a series hybrid less efficient than a parallel one? Because the ICE always has to go through the battery?

I'm still digesting it, but this comparison of series vs. parallel PHEVs seems to cover all the bases.

xxx, and I thought the Volt wasn't a plug-in. It looks like it's a plug-in with an ICE.

 

[_xxx_]

Yeah, I klinda remember the first news where it said it's supposed to be electric only and with a combustion engine for Europe.

(btw. to avoid confusion, ICE are high-speed trains in germany).

 

[Sxotty]

Pete it is two things the conversions:
Heat -->motion-->electricity--> motion in a series
Heat -->motion+electricity--> motion in a parallel
And the fact that you have a ton of batteries you are hauling around. That link you have also has one major oversight that keeps getting propagted and I don't know why. It was even an error in the model put out by the national labs, but was rectified last fall finally.

Your link says

Maximum EV/battery power (kW) 	100 	50 	(50%) 	100 	(200%) 	50
Battery size (kWh) 		16 	5.2  		5.2 		16

You cannot pull an arbitrary amount of power from a battery. If you have 16kWh of batteries you should be able pull 3 times the power as from the 5.2kWh battery (called a C-rate). This means if you want to actually be able to drive on the battery and not the ICE you need either a very high power chemistry, or you need more batteries. Battery makers now are varying the electrode thickness to modify the properties of batteries to try and deal with this problem. Thus you can buy a special high power battery for low energy PHEVs/HEVs or a high energy on for EREVs/PHEVs. The only difference is the electrode thickness mostly, but still if you have 16kWh of one type of battery and 4 kWh of the same type you can pull 4 times the power from the first pack w/o damaging the pack. The parallel PHEV concepts are not that great IMO since it cannot actually drive without turning on the ICE to help with acceleration (since they have small battery packs). Series hybrids are neat and elegant in that you can swap the fuel source to anything later (fuel cell, biofuel, whatever we come up with), or just go full electric in the future fantasy land, whereas parallel hybrids are more of a weird concotion where the electric motors are always undersized and so forth. If the Prius was a series then it could easily have been converted to a PHEV, but as you can see from the stats put out after conversion it just isn't up to the task from a mechanical standpoint.




SB the ICE is oversized it will do more than provide charging to the battery. You do not seem to understand what that means. You will still be able to go 70mph and you will still be able to accelerate perfectly fine it will just pull from the battery (even if it is at 30%). The stop there so there is still room to pull if acceleration is needed. Now you could screw it up if you just romped on the accelerator and then coasted to a stop over and over when you were at 30% charge, but otherwise nothing will happen.

 

[Arwin]

The problem over there in the US is that the quality of diesel varies severely, so we always have to develop for "worst case", which makes the cars more expensive and thus less viable. And a diesel car is still somewhat "dirtier" than the Prius etc. although it'll usually rape the Prius mileage-wise.

Isn't rape a bit exaggerated? I don't drive slow, and I currently have 5.1/100 on my display after well over 700km ... What brings the Prius mileage down generally is a combination of short trips and cold weather. In order to have the engine run clean and efficiently, it needs to be warm. In the summer this is easy, but in the winter the Prius will spend extra effort to heat up quickly at the cost of efficiency. The battery will also lose its power more quickly when it's cold. That makes the mileage vary (for me at least) from about 5.1 in the summer to 5.6 in the winter, especially on short trips. If I stick to driving longer trips (100km or more) then it matters much less, and I get 5.3 or better and the difference seems more due to winter tires.

More interestingly for me, my lease tax is going down again next year, from 14% to 10%. And another form of tax is scrapped for it completely. It's working though - a lot more hybrids and co are coming, including an interesting Seat, and of course the Volt, and competition is heating up nicely.

 

[Simon F]

Pete it is two things the conversions:
Heat -->motion-->electricity--> motion in a series
Heat -->motion+electricity--> motion in a parallel.

With the 2nd scenario, how much energy is lost in a standard car drive train i.e. clutch/gearbox/differential (as well as the engine not operating at the the ideal RPM etc), compared to having an alternator directly driven by the engine and so on with a completely electrical system?

 

[Sxotty]

xxx would be better positioned to answer that. I have seen numbers around 80% efficiency in the drivetrain bandied about though, but I don't personally know.

 

[_xxx_]

Sorry, I'm not familiar with exact efficiency figures and such, I don't deal much with mechanics and hydraulics. I know from my gearbox colleagues that the parallel system has its own culprits and many negatives as well, but I don't know the specifics. I overheard that the combustion engine in a regular car has about 30% efficiency alltogether, while purely electrical cars should be >90%.

The hybrids are the worst in that comparison, because they're being measured with an empty battery to begin with.

Isn't rape a bit exaggerated? I don't drive slow, and I currently have 5.1/100 on my display after well over 700km ...

In the city with lots of starts/stops etc. maybe, but do a constant freeway drive for 700km and check the consumption then. It'll have the consumption of the non-hybrid with a similar engine, in fact even higher due to additional weight etc.

 

[Sxotty]

No worries xxx, btw the regen braking numbers I have seen are lower than 90%. And it depends how you measure it. The batteries are >95% efficient round trip, but that is DC-DC. If you include the charger: grid--> battery--> DC it will be lower depending on the quality of the inverter used. Electricity is cheap so there is little incentive to spend lots of money there keeping efficiency high. I think just from grid --> battery--> DC will be around 90% efficient, but it just depends on choices made (think of all the wall warts in our houses). Then you have the losses in the actual electric motor whatever they are (that is something I would be curios to know honestly).

SB is this where you got your information btw? http://www.caranddriver.com/news/car/09q2/2011_chevrolet_volt_first_drive-car_news

That article has some things that are assumptions, incorrect, or not documented anywhere else. It says that the ICE will not be hooked to the battery for example which contradicts everything I have seen. The info I have seen suggests the ICE will actually slowly recharge the battery once it kicks on. It says 100hp out of 150 hp roughly which is not half the original power, but instead a 33% loss. It is just the estimate that they pulled out of their nether regions. That is why I said it is possible that you would lose top speed, but acceleration would not change from electric only mode, in fact it could theoretically increase actually (though you are still limited by the motors themselves).

 

[Arwin]

In the city with lots of starts/stops etc. maybe, but do a constant freeway drive for 700km and check the consumption then. It'll have the consumption of the non-hybrid with a similar engine, in fact even higher due to additional weight etc.

Constant freeway drive for 700km (well, in sessions of over 200km each anyway) gives me 1l for 19km, at a constant speed of mostly 114-120 (GPS measured) km/h (remember I don't live in Germany ). There are frequent sections where I can't do more than 90 km/h though and at that speed I get well over 20km per liter.

Some of the things helping here are (relatively) low air resistance (0.26 I believe) but also easy to forget that the car has very little braking on engine, and the braking on engine it does do (it used to have none in the first Prius designs, but that freaked people out) is also regenerative.

 

[Simon F]

xxx would be better positioned to answer that. I have seen numbers around 80% efficiency in the drivetrain bandied about though, but I don't personally know.

Sorry, I'm not familiar with exact efficiency figures and such, I don't deal much with mechanics and hydraulics.

It might be lower than that. An (uncited) quote on wikipedia seems to suggest a loss of 50% in one instance. Quite scary, really.

[update] Hmmm it then goes on to say 10-20% loss so I'm confused.

 

[Sxotty]

Simon maybe you could estimate it by checking HP against WHP ratings or something like that. The 20% loss would match the 80% efficiency I have heard, but that doesn't make it true either. I guess the next logical question is what is the alternator/generator efficiency. Are they using AC or DC motors btw? AC motors are more efficient and powerful/ weight I believe, but you then have yet another inversion from DC to AC, of course if it could use the same inverter it would be valueable as an incentive to make it efficient instead of some crappy inverter. (Grid electricity is cheap, but battery electricity you are driving about with is not cheap). The wikipedia thing says that it is the fault of the tires, but rolling resistance isn't that high really so I am unsure what they mean. It might apply equally to electrics though whatever it is referring to (though I think it is incorrect that most of the resistance is from the tires, I could be wrong I should check the actual numbers, but I do know RR is far lower than aerodynamic losses at speed).

 

[Scott_Arm]

... It says that the ICE will not be hooked to the battery for example which contradicts everything I have seen. The info I have seen suggests the ICE will actually slowly recharge the battery once it kicks on...

This is my understanding. Once the battery drains to a certain level, the ICE kicks on and begins recharging the battery. Once it is charged to a certain level, it shuts off and the car continues to run off the battery until it needs to be recharged again.

 

[Arwin]

The wikipedia thing says that it is the fault of the tires, but rolling resistance isn't that high really so I am unsure what they mean.

I thought this too, but there was a science program the otherday suggesting otherwise. It discussed how braking distance is by far the most dependent on the hardness of the tire as well as the amount of tire touching the surface. Trucks easily brake as fast as regular cars, and weight is hardly a factor.

Now I'm not 100% sure if this applies there too, but in the end it makes a lot of sense - imagine that you put a car in motion at 120km/h on skates or whatever. How long would it take to stop versus a car with regular tires on a normal road? (both not braking). The heavier the car (and cars are pretty heavy to begin with), the less wind resistance is going to factor much into it, especially with cars being fairly aerodynamic to begin with. And how much you inflated your tires also has a surprising amount of influence on your power consumption versus everything else.

 

[Sxotty]

Force=N*Crr
Where Crr is the coefficient of rolling resistance as can be found here
http://onlinepubs.trb.org/Onlinepubs/sr/sr286.pdf

Important point is there is nothing about velocity there so it is less and less important at higher speed.