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Old 11-28-2010, 10:54 PM   #21 (permalink)
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Originally Posted by roflwaffle View Post
I can't believe they only pull 35mpg city in charge sustaining mode. Even a Fusion hybrid can pull 41mpg city and that's a full size car. Was engineering a smaller two-mode hybrid system or licensing some of Toyota's stuff really that hard?
That's not really a fair comparison because in city driving the fusion gets the benefit of the electric motor. A better comparison would be to the fusion highway rating of 34mpg. Volt gas only mileage is 37mpg though they don't say whether its city, highway, or mixed.

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Old 11-28-2010, 11:26 PM   #22 (permalink)
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It's fair AFAIK, both are running in charge sustaining mode. The Fusion gets worse highway mileage because it's a fullsize car, not a compact, but it should also get worse city mileage. The problem with the Volt is that running everything through to a generator, then converting that back to mechanical power via the motor reduces efficiency by ~15%-20%, and the single speed trans for he electric motor hurts a bit too (~5+%). If they sent mechanical power directly from the engine to the wheels in charge sustaining mode they would do a lot better than the Fusion hybrid and be very close to a Prius.
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Old 11-29-2010, 12:05 AM   #23 (permalink)
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Originally Posted by roflwaffle View Post
It's fair AFAIK, both are running in charge sustaining mode. The Fusion gets worse highway mileage because it's a fullsize car, not a compact, but it should also get worse city mileage. The problem with the Volt is that running everything through to a generator, then converting that back to mechanical power via the motor reduces efficiency by ~15%-20%, and the single speed trans for he electric motor hurts a bit too (~5+%). If they sent mechanical power directly from the engine to the wheels in charge sustaining mode they would do a lot better than the Fusion hybrid and be very close to a Prius.
I both agree and disagree. I think the Volt should either use a system like all the other hybrids and direct-drive the wheels (especially with the physical connection already there), or even better: have the ICE completely disconnected from the wheels, and run it as a fixed output generator, running at peak efficiency all of the time, and just dumping excess power in the battery pack. Once the batteries are at a set charge level, the motor can switch off (like pulse and glide).

The latter is how I originally thought the Volt would work, as it makes a lot more sense than the super complex set up they have now.
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Old 11-29-2010, 12:48 AM   #24 (permalink)
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Originally Posted by endurance View Post
I think a lot of people are hooked on the idea of never having to buy gas again. However, I think the first time they get a $400 electric bill they just might have second thoughts.
To use $400 worth of electricity you would have to drive the volt 8695 miles, to drive the same distance on gasoline would cost you over $700.
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Old 11-29-2010, 02:32 AM   #25 (permalink)
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I both agree and disagree. I think the Volt should either use a system like all the other hybrids and direct-drive the wheels (especially with the physical connection already there), or even better: have the ICE completely disconnected from the wheels, and run it as a fixed output generator, running at peak efficiency all of the time, and just dumping excess power in the battery pack. Once the batteries are at a set charge level, the motor can switch off (like pulse and glide).

The latter is how I originally thought the Volt would work, as it makes a lot more sense than the super complex set up they have now.
The latter is how the Volt works more or less IIRC. Instead of just having one discrete state they have more than one depending on how much power the motor needs. There is a slight efficiency increase by only operating the Volt at whatever different states, but it's small compared to the drop in efficiency from generating efficiency to feed to the motor instead of just going from the engine to the wheels.
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Old 11-29-2010, 04:49 AM   #26 (permalink)
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Originally Posted by roflwaffle View Post
The latter is how the Volt works more or less IIRC. Instead of just having one discrete state they have more than one depending on how much power the motor needs. There is a slight efficiency increase by only operating the Volt at whatever different states, but it's small compared to the drop in efficiency from generating efficiency to feed to the motor instead of just going from the engine to the wheels.
I suspect that having direct drive instead of the transmission would more than make up for the loss. Fixed output generators are much more efficient than variable output as they run at the most efficient speed. An hybrid car is a perfect application for it as the alternator can be set up to load the system at its most efficient level. As I understand it, the Volt only provides the amount of electricity needed to power the wheels + a bit extra in case of steep hills, so it cannot always be running the gasoline engine at peak efficiency.

Regardless of which is actually better, I agree that GM made the wrong decision. Of the two sensible solutions (true series hybrid or Prius-like hybrid), they managed to combine the worst bits (having a transmission and going gasoline -> rotation -> electric -> rotation).
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Old 11-29-2010, 11:51 AM   #27 (permalink)
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This peak demand charge will sour most businesses allowing folks to recharge EV's at work. I spoke with one business property manager who said he would turn off the circuit breakers for the charging stations in his parking garage. Imagine driving to work, and not being able to recharge for the trip home?
Depends on the employer, though. Some might decide to cover the parking lot with solar panels, like this: http://www.nytimes.com/2010/11/26/sc...me&ref=science

Not every employer focuses on the short-term nickel & dime, or tries to squeeze its employees. For instance the large computer company I once worked for, which keeps about a thousand acres surrounding its Bay Area research lab as a wildlife preserve. I'm pretty sure they'll be putting in EV charging stations before too long, if they haven't already.
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Old 11-29-2010, 02:10 PM   #28 (permalink)
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Originally Posted by roflwaffle View Post
It's fair AFAIK, both are running in charge sustaining mode.
If the battery pack SOC on both vehicles was the same pre/post test then I suppose that its a fair comparison, but I don't know if that's a requirement for fuel economy testing.
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Old 11-29-2010, 02:12 PM   #29 (permalink)
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I suspect that having direct drive instead of the transmission would more than make up for the loss. Fixed output generators are much more efficient than variable output as they run at the most efficient speed. An hybrid car is a perfect application for it as the alternator can be set up to load the system at its most efficient level. As I understand it, the Volt only provides the amount of electricity needed to power the wheels + a bit extra in case of steep hills, so it cannot always be running the gasoline engine at peak efficiency.

Regardless of which is actually better, I agree that GM made the wrong decision. Of the two sensible solutions (true series hybrid or Prius-like hybrid), they managed to combine the worst bits (having a transmission and going gasoline -> rotation -> electric -> rotation).
Do you have any sources? Direct drive instead of a transmission only frees up ~5-10% depending on the transmission, and some hybrids are practically direct drive anyway IIRC (Toyota and licensing their patents). Maybe for small engines fixed output generators are significantly more efficient, but for hybrid automotive engines efficiency doesn't vary a lot, especially over the speeds/loads the engine is operating most of the time. The drop in efficiency from converting everything to electricity and then back to mechanical power via a motor is way more than any gain from running an engine at whatever discrete states. The proof is in the pudding really. The Volt should at least do better in the city than the heavier/larger fusion hybrid, but it does significantly worse because it is a series hybrid.
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Old 11-29-2010, 02:16 PM   #30 (permalink)
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If the battery pack SOC on both vehicles was the same pre/post test then I suppose that its a fair comparison, but I don't know if that's a requirement for fuel economy testing.
It's a requirement AFAIK. Obviously 30% SOC for the Volt is way more than 30% SOC for a normal hybrid, so they don't use an arbitrary point, but they do start where both vehicles will run exclusively in charge sustaining mode IIRC.

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