Article Comments - 2011 Chevrolet Volt First Look

46 messages, Last post on Oct 22, 2008 at 4:38 AM

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What is this discussion about? Chevrolet Volt, Electric Cars, Future Vehicle, Sedan

2011 Chevrolet Volt First Look - The 2011 Chevrolet Volt is both more conventional than you might have been lead to believe and quite a bit more advanced than most potential buyers will know. (more)

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#17 of 46 Re: 40 Miles ? [coldcranker] by tpe Sep 25, 2008 (5:06 am)
Replying to: coldcranker (Sep 24, 2008 8:16 pm) I realize there will always be conversion losses. The one benefit is that the ICE will only operate at it's peak efficiency. When the ICE is directly powering the wheels it operates through a wide power range depending on the driving conditions. I have no idea how big a benefit this is but it will offset some of the conversion losses. I don't think that anyone is claiming the Volt will be the most efficient vehicle on the road once you've exceeded 40 miles. I think it is targeting people that typically don't drive further than 40 miles while also giving them the utility of not being range limited when they occasionally need to drive further. GM believes, and I agree, that this type of driver represents the majority of American motorists. Replies to this message: coldcranker (Sep 25, 2008 10:06 am) tpe (Sep 25, 2008 11:08 am)
#18 of 46 Re: 40 Miles ? [tpe] by coldcranker Sep 25, 2008 (10:06 am)
Replying to: tpe (Sep 25, 2008 5:06 am) tpe said: "The one benefit is that the ICE will only operate at it's peak efficiency. " I previously thought that until all the talk (from GM) about how the Volt will not recharge the batteries using the engine after the initial battery charge is depleted. If you think about that, and read Post #366 (peralta) and #16 here, then you begin to realize that the engine may not be allowed to run at one RPM (sweet spot), or even a narrow range of RPMs near the sweet spot. Do this simulation: You're in a Volt. You have just depleted your battery charge so you hear the engine come on, and you're cruising at 60 mph down the highway. Now you come to a stop, and the engine must also throttle down, since power is not flowing to the batteries much, if at all, and, of course, you don't need power to move right now either. Now you hit the accelerator pedal to go again, and the engine must throttle up to meet power demands. If the engine would be allowed to run steady at its sweet spot, even when stopped in traffic, some of the power must go to the batteries, as all that energy has to go somewhere, but GM has chosen not to burn gasoline to recharge the batteries (maybe a little charging going on). But if you read peralta's post 366, you'll understand that it is very inefficient to use gasoline to recharge the batteries. However, its not too terribly inefficient (about 80%) to generate electricity on demand to power the electric motor. That 80% isn't as good as getting power to the wheels through a good transmission (95%) but in the big picture, its not bad. For those taking a long trip (vacation) in the Volt, I would expect no better than 30 MPG or so from a 1.4L engine with 20% "transmission" losses running the vehicle. The Volt will be great as an around-town car, but not on long trips. Railroad trains are diesel-electric in that they operate with no mechanical transmission, only a diesel engine running a generator, attached to electric motors to propel the train, just like the Volt after battery depletion. I suppose you could use the depleted batteries on the Volt for short bursts of power, recovered in regenerative braking and small amounts of engine charging. This is similar to the hydraulic hybrid concept, where hydraulic accumulators (analagous to batteries here) store short bursts of energy, and those hybrid vehicles gain 50% MPG in city driving, such as in UPS trucks and garbage trucks. Hydraulic hybrids will revolutionize stop-n-go trucks in the future. The Volt could do this and offload the engine during hard acceleration for short periods of time and probably do OK in overall efficiency, allowing the engine to reduce its load during acceleration. Replies to this message: tpe (Sep 25, 2008 11:08 am)
#19 of 46 Confirmed the Volt's engine stops at stoplights by coldcranker Sep 25, 2008 (10:53 am)
OK, I did a little looking around on the web, and the Volt's engine will throttle down and then maybe turn off at stoplights. "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." -- click here for the link Thats why I think the hope of running the engine in/near the sweet spot load/RPM combination is dashed. Without significant caching of energy into the batteries, the electric generator/motor functions as an inefficient transmission (batteries depleted). Replies to this message: tpe (Sep 25, 2008 11:36 am)
#20 of 46 Re: 40 Miles ? [coldcranker] by tpe Sep 25, 2008 (11:08 am)
Replying to: coldcranker (Sep 25, 2008 10:06 am) I previously thought that until all the talk (from GM) about how the Volt will not recharge the batteries using the engine after the initial battery charge is depleted. I'm not sure where this is coming from. The Chevy Volt website specifically says that once you've gone past 40 miles the onboard power supply will "recharge" the battery. volt Is the website incorrect? When you come to a stop I'd expect the Volt ICE to shut down. When you restart the engine will return to running within a narrow range around the sweet spot and draw any additional needed power from the battery pack. Whatever power is drawn from the battery pack will be returned by the ICE recharging it. However inefficient this may be it can't be all that different from how the Prius and other hybrids keep their batteries within a certain state of charge. Yes the Prius accomplishes a portion of it's recharging through regenerative braking, so will the Volt, but that can't possibly account for all of it. So where would the rest of the recharging come from in a Prius if it isn't the ICE? After 40 miles the big difference I see between the Prius and the Volt is that the Prius ICE directly drives the wheels and the Volt's ICE will generate electricity to drive the motors that drive the wheels, adding a conversion loss. And I agree that the Prius is more efficient here but even using your numbers I'm not sure how you get to 30 mpg once the Volt has gone past 40 miles. The upcoming Honda Insight is reported to get over 60 mpg. The next generation Prius, with upgraded batteries, is also reported to get over 60 mpg. If this is with a 5% transmission loss then just deduct another 15% for the Volt. It comes out to ~50 mpg. I think the end result will be that the Volt uses less gas until you get to trips of over 200 miles. In my case I probably make a couple trips a year over that distance. So on 99% of my trips the Volt would use less fuel. The other 1% of the time I would have been better off with a Prius or Insight. Now the plug-in Prius could end up being the best of both worlds if they give it a comparable all electric range and a more powerful motor to adequately support an all electric mode.
#21 of 46 Re: Confirmed the Volt's engine stops at stoplights [coldcranker] by tpe Sep 25, 2008 (11:36 am)
Replying to: coldcranker (Sep 25, 2008 10:53 am) That was a good link. I don't see this new information as a negative but a positive. I think anyone who's been following the Volt should be happy that they have chosen to do it this way. I was under the impression that all the power generated by the ICE went straight to the battery pack, which was the sole source of power for the motor. You must agree that would have added another conversion loss and have been less efficient. As far as keeping the engine running in the sweet spot range I see this as less of a problem for the Volt than a hybrid like the Prius. The reason being is that the Prius has a much less powerful electric motor, which forces the ICE to operate through a wider range. Another benefit that the Volt will have is the ability to recapture more energy through regenerative braking. This is a result of it's larger battery pack that also uses a different chemistry that allows for higher charge/discharge rates.
#22 of 46 not sure it makes sense by kurtamaxxxguy Sep 25, 2008 (12:09 pm)
I keep wondering what apartment renters are going to with the Volt, especially since Volt cannot recharge its batteries save by regenerative braking. We rarely get outlets in our parking stalls! So it seems the class of owners that can use the Volt is made up of those meeting all 3 conditions below: 1. Homeowners with easily accessed charging points 2. Driving distances not exceeding 40 miles at a time 3. Areas free of "power intensive" needs (hills, very cold, very hot, etc.) Will that class of drivers be enough for GM to actually make money off the Volt? Perhaps, now that the Big 3 have been granted their $25 bil bailout, they won't need to for awhile? Replies to this message: tpe (Sep 25, 2008 12:30 pm) larsb (Sep 25, 2008 12:34 pm) tpe (Sep 25, 2008 2:32 pm) coldcranker (Sep 25, 2008 5:58 pm) and 1 more...
#23 of 46 Re: not sure it makes sense [kurtamaxxxguy] by tpe Sep 25, 2008 (12:30 pm)
Replying to: kurtamaxxxguy (Sep 25, 2008 12:09 pm) The Volt being able to charge itself makes zero sense. Would you ever consider plugging the Volt into a portable gas generator to recharge? Hopefully not. So why would anyone want the onboard generator to do this? I just can't understand all this dissapointment I'm hearing over the Volt not being able to recharge itself. Exactly what benefit would that provide? Replies to this message: larsb (Sep 25, 2008 12:34 pm) tpe (Sep 25, 2008 2:32 pm) coldcranker (Sep 25, 2008 5:58 pm) eaton53 (Sep 26, 2008 1:53 pm)
#24 of 46 Re: not sure it makes sense [tpe] by larsb Sep 25, 2008 (12:34 pm)
Replying to: tpe (Sep 25, 2008 12:30 pm) Am I missing something? I thought EVERYONE (at least at Edmunds who is following the Volt) knows that the on-board engine in the Volt is ONLY THERE TO CHARGE THE BATTERY. It serves no other purpose. It does not drive the wheels. It will be powering no accessories. It's just an on-board electricity generator for the batteries which power the electric motor. Replies to this message: tpe (Sep 25, 2008 2:32 pm) coldcranker (Sep 25, 2008 5:58 pm) eaton53 (Sep 26, 2008 1:53 pm)
#25 of 46 Re: not sure it makes sense [larsb] by tpe Sep 25, 2008 (2:32 pm)
Replying to: larsb (Sep 25, 2008 12:34 pm) I was under the same misconception. It turns out the ICE generator will directly power the electric motor with some power being used to maintain the battery pack at a 30% state of charge. I was glad to hear this but apparently some people are upset because they feel like they've been misled. I wonder if these people would be upset if GM came out and said that contrary to their initial statements claiming a 40 mile all electric range it now looks like this range will be 50 miles? Basically this new information represents a significant improvement over what people like myself originally believed.
#26 of 46 Re: not sure it makes sense [larsb] by coldcranker Sep 25, 2008 (5:58 pm)
Replying to: larsb (Sep 25, 2008 12:34 pm) larsb, As other posters on this and the other Volt forum have mentioned, this GM strategy to prevent the engine from doing much charging of the batteries may be a good thing once you think about it. It was pointed out that charging and discharging the battery is only about 50% efficient (a lot of waste heat). Therefore, let the utility companies charge the battery up each night, and then let the engine just feed amps to the electric motor directly, with only a small amount of charge going to keep the batteries least 30% charge, with some help from regenerative braking. The other discussion I've had is interesting from a fuel economy point of view: Will the engine get to run most of the time at/near optimum load/RPM? If the batteries, once depleted, can muster enough juice to give the electric motor an occasional boost, then the engine would be free to just provide a more steady flow of amps to the motor (similar to hydraulic hybrids), and can stay near optimal load/RPM. That may not be the case, so the engine may be throttled up and down as the electric motor demands more or less power. Thats why I was saying that we can view the generator/motor combo has an inefficient (80%) "transmission", since it performs the same function as a conventional transmission, to get the power from the engine to the wheels. If you run a 1.4L engine through an 80% efficient transmission, then you'll get about 30 MPG on the highway with this 3300 lb Volt. Replies to this message: eaton53 (Sep 26, 2008 1:53 pm)