smkettner
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Re: Revised gearing for highway commuters?

Sun Apr 24, 2011 5:46 pm

derkraut wrote:I would imagine that Nissan tried all the stuff you guys are talking about, when they developed/tested the Leaf. :?:

x2,

with all the resources of Nissan I am sure a few different motors and ratios were tried in various conditions.
The last thing I want is a two speed transmission. The 90mph top speed is way beyond what I need.
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edatoakrun
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Re: Revised gearing for highway commuters?

Sun Apr 24, 2011 6:27 pm

Herm wrote:
edatoakrun wrote: But, unless I'm missing something, looking at that efficiency curve, I cant help thinking that The LEAF's overall efficiency could be improved-a few percent overall?-by a variable final drive ratio, even as simple as two "speeds".



Are we looking at the same graph?.. there is a possibility of improving eff below 40mph, but little power is consumed at those slow speeds anyways, it may gain you about 1/10 mile range if you drove at 30mph (that was a WAG).. it is already optimized for speeds from 40-80mph with its single speed transmission.


Yes, and the rest of my post you quoted reads:

"Obviously, Nissan decided cost and complexity outweigh benefits on the LEAF. I wonder if Nissan is considering it, though, for future higher cost and performance cars, such as the ESFLOW based on the LEAF drive-train?"

Clearly the LEAF motor and the rest of the drive train are designed to maximize performance in an economy car. I doubt Nissan would re-engineer the drive train for a performance car produced in far lower numbers. I think that, in a vehicle class where 0-60 performance, and high speed capability (how many buyers of $50 k sports cars likely to be happy with a two digit top speed?) in addition to vehicle range, are all "selling points", a variable final drive ratio, might be an effective modification.

Just an (off-topic) thought.
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bowthom
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Re: Revised gearing for highway commuters?

Sun Apr 24, 2011 6:33 pm

Hello,
Somewhere I read 8:1 final ratio
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nader
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Re: Revised gearing for highway commuters?

Mon Apr 25, 2011 12:43 am

Granted I am new to EV's and still have a lot to learn but doesn't a motor turning at lower RPM consume less electricity? Hence all of these newer cars having a tall top gear to improve mileage at highway speeds. I imagine Nissan chose a gear ratio that gave a decent top speed and acceleration while staying within the motors efficiency range. My question is if I was willing to give up some acceleration on the bottom end could I make enough of a difference in power consumption on the top end by having the motor turn at a lower RPM.

As far as tire size changes that isn;t going to make much difference. You can't go with a much larger overal diameter than the stock 25" diameter before you'll run into clearance issues with struts, fenders etc.

jkirkebo
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Re: Revised gearing for highway commuters?

Mon Apr 25, 2011 1:22 am

nader wrote:Granted I am new to EV's and still have a lot to learn but doesn't a motor turning at lower RPM consume less electricity?


No, it doesn't.

nader
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Re: Revised gearing for highway commuters?

Mon Apr 25, 2011 1:39 am

So aside from aero mods and weight reduction what could be done to the motor/gearing to increase range at highway speeds? I'm not saying it has to be without compromise either. I just want to know what will make a difference.

-nader

jkirkebo
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Re: Revised gearing for highway commuters?

Mon Apr 25, 2011 3:42 am

nader wrote:So aside from aero mods and weight reduction what could be done to the motor/gearing to increase range at highway speeds? I'm not saying it has to be without compromise either. I just want to know what will make a difference.

-nader


There's just about nothing you can do to the gearing or motor to get a meaningful range increase. What can easily increase or decrease your range is your driving style, use of AC/heater etc.

IOW; mod the driver, not the car ;)

Herm
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Re: Revised gearing for highway commuters?

Mon Apr 25, 2011 5:47 am

A mod that would work would be an extra aggressive ECO mode, the faster you speed over 55mph the harder the gas pedal pushes against your foot.. after a while (or if you get a cramp) you get the hint and slow down :)

edatoakrun
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Re: Revised gearing for highway commuters?

Mon Apr 25, 2011 6:56 am

ICEV cars run at very low levels of energy efficiency at ALL speeds, so the same range/efficiency penalty produced by air resistance at higher speeds is often less apparent to the driver, than with a BEV. Operating in the most efficient narrow RPM range for an ICEV engine will give much greater efficiency, so, if properly geared, an ICEV vehicle may lose little range/mpg by increasing speed up to (legal) freeway speeds, and final drive ratios are often set to realize this benefit.

Unlike an ICEV, the LEAF drive train is within a few percent of maximum efficiency in a very broad range, from about 4,000 to 9,000 RPM, which if i correctly recall the calculations done by others previously, is about 35 to 85 mph. You could shift the LEAF efficiency curve to the right (higher speed) by altering the final drive ratio, but the tiny gain in drive train efficiency, would only be at very high speeds, and be nearly insignificant.

If you take a look at the drive train efficiency curve drees posted yesterday he took from P 17/18 here:

http://www.electricauto.org/resource/re ... e_2_11.pdf

Look at the vertical scale on the same chart. It seems the LEAF is only significantly lower than optimum efficiency in high torque demand/low speed operation. Shifting the curve to the right by altering the final drive ratio would decrease the efficiency in these conditions, probably more than offsetting high-speed gains.

So at low speed, a light foot is your best "range extender", and the best "range extender" at high speeds, is avoiding high speeds, and the large aerodynamic drag penalty incurred.

As I said in your "drive home" thread, for trips exceeding single charge length (until we get DC charging) the slower you drive, the faster you will get to your destination.


nader wrote:Granted I am new to EV's and still have a lot to learn but doesn't a motor turning at lower RPM consume less electricity? Hence all of these newer cars having a tall top gear to improve mileage at highway speeds. I imagine Nissan chose a gear ratio that gave a decent top speed and acceleration while staying within the motors efficiency range. My question is if I was willing to give up some acceleration on the bottom end could I make enough of a difference in power consumption on the top end by having the motor turn at a lower RPM.

As far as tire size changes that isn;t going to make much difference. You can't go with a much larger overal diameter than the stock 25" diameter before you'll run into clearance issues with struts, fenders etc.
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TomT
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Re: Revised gearing for highway commuters?

Mon Apr 25, 2011 8:50 am

Non-diesel ICE cars usually are most efficient at higher throttle openings due to reduced vacuum pumping losses. (Some engines, such as BMW's Valvetronic, no longer uses conventional throttle butterflies and this does not apply to them to the same degree.) Thus, that is why they try to gear as high (numerically low) as possible at high way speeds. 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. Speed and load affects both of their mileage similarly.


edatoakrun wrote:ICEV cars run at very low levels of energy efficiency at ALL speeds, so the same range/efficiency penalty produced by air resistance at higher speeds is often less apparent to the driver, than with a BEV. Operating in the most efficient narrow RPM range for an ICEV engine will give much greater efficiency, so, if properly geared, an ICEV vehicle may lose little range/mpg by increasing speed up to (legal) freeway speeds, and final drive ratios are often set to realize this benefit.
Last edited by TomT on Mon Apr 25, 2011 12:55 pm, edited 1 time in total.
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