edatoakrun
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Re: highway speed efficiency

Wed Sep 12, 2012 7:00 am

Pipcecil wrote:As a leaf and a volt owner I can say that the volt in all EV mode, handles the highway speeds significantly better than the leaf. I attribute this a lot to aerodynamic efficiency. The leaf is a larger vehicle, so it will create more drag than the volt. In addition the volt has a very low ground clearnance - my wife scraps bottom every day leaving the driveway. She never had before even when she owned a two-seater sports car. The lower profile is a big aerodynamic saver at high speeds, which is why tesla has the air suspension thingie that lowers the vehicle at high speeds and semi trucks us that plastic paneling to cover up under the trailers.

Those two together I think make a good difference. As for the powertrain, I still think the leaf's is more efficient (i.e. see the EPA's MPGe, 94 vs 99). The higher your speed, the less effiecient (exponential) really points to the aerodynamics of the car.
And also, because the Volt is quite a bit heavier than the LEAF, it will get less of an increase in efficiency by driving more slowly than the LEAF does, and the extra weight will produce a larger decrease in efficiency in "stop and go" traffic or on roads with ascents and descents requiring regenerative braking, than it will in more level and constant-speed driving.

So, while on trips in your LEAF where driving speed averages 35 rather than 70 mph, you typically see a reduction in range of almost 50%, in the Volt, you typically only see a reduction of what-maybe about 40%?
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RegGuheert
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Re: highway speed efficiency

Wed Sep 12, 2012 10:48 am

adric22 wrote:So the question is, why? Is it a matter of aerodynamics? Or is there something about the Leaf drivetrain that makes it inefficient at those speeds?
I've seen this covered in one of the GM deep dive videos on the Volt drivetrain. Basically, the Volt has multiple operating modes, each of which is provides the optimum efficiency for a different range of speeds. The mode used for highway driving is optimized around 70 MPH, IIRC.

The LEAF, OTOH, is designed from the standpoint of simplicity. By using a singe reduction gear, the weight and complexity of the transmission system is minimized, but the trade off is that efficiency is optimized at just a singe speed. I believe I have read that the peak drivetrain efficiency (without aerodynamics) for the LEAF is aroun 45 MPH. So as you move from 45 MPH to 70 MPH in the LEAF, you not only increase aerodynamic losses, but you also move down the drivetrain efficiency curve. How far down you get from the peak of 95% I do not know.

I'll post links to the data if I can locate it.

Chevy Volt Powertrain
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
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Stanton
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Re: highway speed efficiency

Wed Sep 12, 2012 11:43 am

RegGuheert wrote: The LEAF, OTOH, is designed from the standpoint of simplicity. By using a singe reduction gear, the weight and complexity of the transmission system is minimized, but the trade off is that efficiency is optimized at just a singe speed. I believe I have read that the peak drivetrain efficiency (without aerodynamics) for the LEAF is aroun 45 MPH. So as you move from 45 MPH to 70 MPH in the LEAF, you not only increase aerodynamic losses, but you also move down the drivetrain efficiency curve. How far down you get from the peak of 95% I do not know.
So now I've read/heard (over time) that the MOST energy efficient speed for the Leaf is anything from 20mph->45mph. Will the real speed please stand up?
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edatoakrun
Posts: 5222
Joined: Thu Nov 11, 2010 9:33 am
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Re: highway speed efficiency

Wed Sep 12, 2012 11:46 am

RegGuheert wrote:
adric22 wrote:So the question is, why? Is it a matter of aerodynamics? Or is there something about the Leaf drivetrain that makes it inefficient at those speeds?
I've seen this covered in one of the GM deep dive videos on the Volt drivetrain. Basically, the Volt has multiple operating modes, each of which is provides the optimum efficiency for a different range of speeds. The mode used for highway driving is optimized around 70 MPH, IIRC.

The LEAF, OTOH, is designed from the standpoint of simplicity. By using a singe reduction gear, the weight and complexity of the transmission system is minimized, but the trade off is that efficiency is optimized at just a singe speed. I believe I have read that the peak drivetrain efficiency (without aerodynamics) for the LEAF is aroun 45 MPH. So as you move from 45 MPH to 70 MPH in the LEAF, you not only increase aerodynamic losses, but you also move down the drivetrain efficiency curve. How far down you get from the peak of 95% I do not know.

I'll post links to the data if I can locate it.

Chevy Volt Powertrain

IIRC, there is almost no reduction in the LEAF drive train efficiency anywhere between~25 and ~75 MPH.

Who has the link to the LEAF drive train efficiency chart?

There are several threads (somewhere) on MNL, discussing why more than one final drive ratio is of relatively little value for EVs.
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edatoakrun
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Re: highway speed efficiency

Wed Sep 12, 2012 11:49 am

Stanton wrote:
RegGuheert wrote: The LEAF, OTOH, is designed from the standpoint of simplicity. By using a singe reduction gear, the weight and complexity of the transmission system is minimized, but the trade off is that efficiency is optimized at just a singe speed. I believe I have read that the peak drivetrain efficiency (without aerodynamics) for the LEAF is aroun 45 MPH. So as you move from 45 MPH to 70 MPH in the LEAF, you not only increase aerodynamic losses, but you also move down the drivetrain efficiency curve. How far down you get from the peak of 95% I do not know.
So now I've read/heard (over time) that the MOST energy efficient speed for the Leaf is anything from 20mph->45mph. Will the real speed please stand up?
I'd guess about 15 mph on a level route.

Got 10-12 free hours to give it a try?
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LEAFfan
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Re: highway speed efficiency

Wed Sep 12, 2012 12:07 pm

edatoakrun wrote:I'd guess about 15 mph on a level route.
Got 10-12 free hours to give it a try?
I've already done an hour flat loop at a steady 15mph (posted last year), and hit 9.1m/kW h on the center console since the dash only goes to 8.0.
On a Sanctioned Efficiency Run last March, I averaged 8.5m/kW h on a 151 mile loop (not all flat) on one charge with an 8-10% capacity loss. I tried to drive about 25mph most of the time and almost the whole distance the power stayed in the 'N' circle.
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TickTock
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Re: highway speed efficiency

Wed Sep 12, 2012 12:12 pm

I was able to get 11.5 mpkwh (on center console) at 9mph doing laps.

http://www.mynissanleaf.com/viewtopic.p ... h&start=72
LEAFfan wrote:
edatoakrun wrote:I'd guess about 15 mph on a level route.
Got 10-12 free hours to give it a try?
I've already done an hour flat loop at a steady 15mph (posted last year), and hit 9.1m/kW h on the center console since the dash only goes to 8.0.
On a Sanctioned Efficiency Run last March, I averaged 8.5m/kW h on a 151 mile loop (not all flat) on one charge with an 8-10% capacity loss. I tried to drive about 25mph most of the time and almost the whole distance the power stayed in the 'N' circle.

edatoakrun
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Re: highway speed efficiency

Wed Sep 12, 2012 12:40 pm

TickTock wrote:I was able to get 11.5 mpkwh (on center console) at 9mph doing laps.

http://www.mynissanleaf.com/viewtopic.p ... h&start=72
LEAFfan wrote:
edatoakrun wrote:I'd guess about 15 mph on a level route.
Got 10-12 free hours to give it a try?
I've already done an hour flat loop at a steady 15mph (posted last year), and hit 9.1m/kW h on the center console since the dash only goes to 8.0.
On a Sanctioned Efficiency Run last March, I averaged 8.5m/kW h on a 151 mile loop (not all flat) on one charge with an 8-10% capacity loss. I tried to drive about 25mph most of the time and almost the whole distance the power stayed in the 'N' circle.
Do you know what your average speed was, as calculated by drive time?


Sorry, but I've lost (almost) all faith in the dash/nav screen m/kWh numbers.

Mine have increased to the point that they are now straddling ~6.5 m/kWh on trips including climbs over mountain passes...

http://www.mynissanleaf.com/viewtopic.p ... 4&start=30" onclick="window.open(this.href);return false;
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Stanton
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Re: highway speed efficiency

Wed Sep 12, 2012 12:40 pm

Now that's some good data guys!
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RegGuheert
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Re: highway speed efficiency

Wed Sep 12, 2012 12:51 pm

Stanton wrote:So now I've read/heard (over time) that the MOST energy efficient speed for the Leaf is anything from 20mph->45mph. Will the real speed please stand up?
I'm not talking about "the MOST energy efficient speed for the Leaf". I'm discussing the peak efficiency point for the drivetrain. As mentioned, it is a pretty broad curve.
edatoakrun wrote:IIRC, there is almost no reduction in the LEAF drive train efficiency anywhere between~25 and ~75 MPH.

Who has the link to the LEAF drive train efficiency chart?

There are several threads (somewhere) on MNL, discussing why more than one final drive ratio is of relatively little value for EVs.
Here is the link to the paper with drivetrain efficiency for the LEAF: The Nissan LEAF Drive Train

The efficiency plot is found on page four of that presentation. Sorry, I do not know how to extract it to post it here. But I know it was posted somewhere on this forum previously.

As you say, the efficiency of the LEAF drivetrain is broad and flat. It only varies from about 85% to 95%. over the entire range of operation.
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

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