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Re: Revised gearing for highway commuters?

Posted: Mon Apr 25, 2011 9:13 am
by edatoakrun
mogur wrote: By the way, the relative useable efficiency of a ICE and BEV are not that much different if you look at the numbers carefully. It is just that the ICE has a higher level of residual and overall energy loss.
Please explain your terms.

Re: Revised gearing for highway commuters?

Posted: Mon Apr 25, 2011 10:16 am
by Herm
The explanation has lots to do with mass quantities of beer :)

Re: Revised gearing for highway commuters?

Posted: Mon Apr 25, 2011 12:52 pm
by TomT
Let's look at it this way:

On my Leaf, I climb a given long hill near home and my efficiency drops to about 2 miles per KwH from my normal 4.5.

On my ICE, which is a little lighter, and which has an instantaneous consumption display, climbing the same hill causes efficiency to drop from about 28MPG to about 12MPG.

Thus, the relative drop in efficiency as a function of how far I can go with the respective fuel is about the same for both vehicles.
edatoakrun wrote:
mogur wrote: By the way, the relative useable efficiency of a ICE and BEV are not that much different if you look at the numbers carefully. It is just that the ICE has a higher level of residual and overall energy loss.
Please explain your terms.

Re: Revised gearing for highway commuters?

Posted: Mon Apr 25, 2011 1:06 pm
by nader
I understand the whole 4-9000rpm motor efficiency thing. In this case it's how much of that electricity is turned into mechanical motion. Are you guys telling me that if I were to put this motor on a dyno and run it at 4,000 rpm and then at 9,000rpm that it's consuming the same amount of electricity? Conventional wisdom tells me that is not the case. Please school me.

Side note: Because of this motor efficiency and lack of transmission I am guessing that drivetrain losses are much lower than a traditional ICEV.

-Nader

Re: Revised gearing for highway commuters?

Posted: Mon Apr 25, 2011 1:21 pm
by smkettner
nader wrote:I understand the whole 4-9000rpm motor efficiency thing. In this case it's how much of that electricity is turned into mechanical motion. Are you guys telling me that if I were to put this motor on a dyno and run it at 4,000 rpm and then at 9,000rpm that it's consuming the same amount of electricity? Conventional wisdom tells me that is not the case. Please school me.
Considering it just sits on two bearings 9000 will not take much more power than 4000.

Now an ICE will take a lot more power to turn 9000 vs 4000 (assuming it stays together).
Ever try to turn an ICE by hand? Ever turn an electric motor?

Re: Revised gearing for highway commuters?

Posted: Mon Apr 25, 2011 1:53 pm
by DaveEV
nader wrote:I understand the whole 4-9000rpm motor efficiency thing. In this case it's how much of that electricity is turned into mechanical motion. Are you guys telling me that if I were to put this motor on a dyno and run it at 4,000 rpm and then at 9,000rpm that it's consuming the same amount of electricity? Conventional wisdom tells me that is not the case. Please school me.
Just look at the efficiency plot (far better than your typical dyno plot and even better than most BSFC plots you see for engines which typically only show BSFC at WOT) for the LEAF which I posted earlier from the SAE article:
http://www.mynissanleaf.com/viewtopic.p ... 124#p84124

One can easily see that peak efficiency (above 93%) is between 4000-8000 rpm at torque levels above 50 Nm and is very flat between those ranges. Below 2000 rpm efficiency is pretty low (<= 85%) at all torque levels and at all rpms efficiency drops off rapidly at torque levels below 25 Nm.

Re: Revised gearing for highway commuters?

Posted: Mon Apr 25, 2011 2:02 pm
by nader
Thanks for the schooling guys. I have hand cranked an ICE. Lot's of internal resistance.

So the bottom line is, lower the cD, drop curb weight or increase pack capacity in order to in increase highway range. (or all of the above). Too bad the Aptera never made it to market. I imagine that has to be much more efficient at highway speeds.

Re: Revised gearing for highway commuters?

Posted: Mon Apr 25, 2011 2:09 pm
by DaveEV
nader wrote:So the bottom line is, lower the cD, drop curb weight or increase pack capacity in order to in increase highway range. (or all of the above).
At highway speeds, anything you can do to lower wind resistance is going to have the biggest effect on range. Curb weight's effect on highway range (provided the road is fairly flat) is next to negligible unless we're talking about 30% reductions here. As it is - easiest thing to do to increase highway range is to slow down!

It won't be long before someone on the forums at ecomodder.com fabs up a boat-tail extension for the LEAF!

Re: Revised gearing for highway commuters?

Posted: Mon Apr 25, 2011 2:22 pm
by edatoakrun
nader wrote:I understand the whole 4-9000rpm motor efficiency thing. In this case it's how much of that electricity is turned into mechanical motion. Are you guys telling me that if I were to put this motor on a dyno and run it at 4,000 rpm and then at 9,000rpm that it's consuming the same amount of electricity? Conventional wisdom tells me that is not the case. Please school me.

Side note: Because of this motor efficiency and lack of transmission I am guessing that drivetrain losses are much lower than a traditional ICEV.

-Nader
A good (if Tesla-centric) general discussion, with illustrative graphics, of BEV efficiency compared to ICE, hybrid, and fuel cell Vehicles, is here:

http://www.teslamotors.com/goelectric/efficiency

The LEAF is consuming much more than 9/4 times the electricity on the road running at 9,000 vs 4,000 rpm, but this is primarily due to the effects of wind resistance at greater speed.

Looking at the Tesla power consumption chart, you can see that each rotation of the wheels on the dyno actually takes less power, at higher engine rpms, corresponding to road speeds up to at least 70 mph. Given the LEAF drive train efficiency chart, it would also appear to be true, up to dyno (wheel speed w/o wind resistance) speeds of about 70 mph.

Interestingly, Tesla originally planned a 2 speed, but later decided it was easier just to rev the damn thing to 14,000 RPM, according to:

http://en.wikipedia.org/wiki/Tesla_Roadster