nader
Posts: 296
Joined: Wed Jul 28, 2010 12:48 pm
Delivery Date: 0- 0-2011
Leaf Number: 1925
Location: Fres-yes

Revised gearing for highway commuters?

Sun Apr 24, 2011 10:07 am

I haven't been able to find the spec on final drive ratio, but i was thinking it might be interesting to have a new ring and pinion cut to lower RPMs at highway speeds. I know wind resitance becomes a bigger issue but I cant help but think that lowering RPMs at highway speeds by 15-20% will increase range. Of course acceleration will suffer but i think its got enough torque that it won't make that much of a diffefence.

Thoughts?

User avatar
TomT
Posts: 10640
Joined: Sun Aug 08, 2010 12:09 pm
Delivery Date: 01 Mar 2011
Leaf Number: 000360
Location: California, now Georgia
Contact: Website

Re: Revised gearing for highway commuters?

Sun Apr 24, 2011 10:11 am

Unlike on an ICE vehicle, it wouldn't make much difference.

nader wrote:I haven't been able to find the spec on final drive ratio, but i was thinking it might be interesting to have a new ring and pinion cut to lower RPMs at highway speeds. I know wind resitance becomes a bigger issue but I cant help but think that lowering RPMs at highway speeds by 15-20% will increase range. Of course acceleration will suffer but i think its got enough torque that it won't make that much of a diffefence.

Thoughts?
Leaf SL 2011 to 2016, Volt Premier 2016 to 2019, and now:
2019 Model 3; LR, RWD, FSD, 19" Sport Wheels, silver/black; built 3/17/19, delivered 3/29/19.

edatoakrun
Posts: 5222
Joined: Thu Nov 11, 2010 9:33 am
Delivery Date: 15 May 2011
Leaf Number: 2184
Location: Shasta County, North California

Re: Revised gearing for highway commuters?

Sun Apr 24, 2011 11:04 am

About the only significant difference, I expect, would be a higher top speed-on a downgrade.

I was going to suggest, that a far cheaper and easily reversible way to test this, would be to get higher-profile tires, to lower freeway RPM.

But that got me wondering about aerodynamic drag. Normally a higher profile tire would, by raising a car, very significantly increase drag. But with the LEAF's smooth underbelly, it might not increase drag a great deal (though increased lift might significantly affect handling if you changed the final drive ratio enough, AND found a grade steep enough to produce very high speeds...).

I owned a Citroen DS21 with an (almost) smooth belly plate, and a hydro pneumatic adjustable suspension, giving it several inches of ride-height adjustment. I don't recall ever driving long distance on the high setting, to check for how much fuel economy or top speed was reduced, though...
no condition is permanent

palmermd
Posts: 2566
Joined: Fri Apr 23, 2010 3:19 pm
Delivery Date: 31 Mar 2011
Leaf Number: 1100011011
Location: Hermosa Beach, CA

Re: Revised gearing for highway commuters?

Sun Apr 24, 2011 11:15 am

mogur wrote:Unlike on an ICE vehicle, it wouldn't make much difference.



+1 it might actually be the opposite. Many times there is a high rpm point where the motor will drop off rapidly in its abitlity to put out power, and the efficiency at that point seems to go up just a little, but for the most part it makes little difference what speed your are running. You'd have to get the motor curves to know.
Michael

Leaf from 31 March 2011 - Traded 18 April 2018 for Tesla Model 3 Unicorn
Driving electric since 1996


Leaf Bar Loss

Herm
Posts: 3765
Joined: Sun May 23, 2010 3:08 pm
Delivery Date: 29 Aug 2012
Location: Timbuktu, Mali

Re: Revised gearing for highway commuters?

Sun Apr 24, 2011 12:05 pm

it would not make a difference, the Leaf's motor has top efficiency over a wide range of RPM. Going to a narrower 185 size tire may reduce your tire drag, also lowering the car should reduced air drag. You should also inflate the tires to the max sidewall ratings.

User avatar
DaveEV
Forum Supporter
Posts: 6234
Joined: Fri Apr 23, 2010 3:51 pm
Location: San Diego

Re: Revised gearing for highway commuters?

Sun Apr 24, 2011 1:03 pm

palmermd wrote:+1 it might actually be the opposite. Many times there is a high rpm point where the motor will drop off rapidly in its abitlity to put out power, and the efficiency at that point seems to go up just a little, but for the most part it makes little difference what speed your are running. You'd have to get the motor curves to know.

The motor curves are published somewhere by an engineering publication - can't find the link right now, but there's a thread somewhere.

Efficiency is at it's peak of appx 95% at load (a bit more than very light throttle) and moderate speed (between 55 mph or so). Efficiency drops to 85% outside of that sweet spot. Note that this doesn't take into account other losses - such as the motor controller or battery losses at higher currents.

Edit: Here's the link to the thread: Nissan LEAF featured in Feb '11 SAE Newsletter and a quick screengrab of the chart.

Image

ENIAC
Posts: 645
Joined: Thu Jan 06, 2011 9:05 pm
Delivery Date: 13 Jan 2011
Leaf Number: 224
Location: Sun Diego, CA USA

Re: Revised gearing for highway commuters?

Sun Apr 24, 2011 1:45 pm

nader wrote:I haven't been able to find the spec on final drive ratio
The LEAFs final drive ratio 7.9377
Myths And Facts About Electric Cars

"The ice doesn't care"
-- WetEV

edatoakrun
Posts: 5222
Joined: Thu Nov 11, 2010 9:33 am
Delivery Date: 15 May 2011
Leaf Number: 2184
Location: Shasta County, North California

Re: Revised gearing for highway commuters?

Sun Apr 24, 2011 2:23 pm

Doesn't look to me like you'll gain much at (legal) freeway speeds by changing the final drive ratio, and would also lose efficiency in low-speed use. 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".

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?
no condition is permanent

Herm
Posts: 3765
Joined: Sun May 23, 2010 3:08 pm
Delivery Date: 29 Aug 2012
Location: Timbuktu, Mali

Re: Revised gearing for highway commuters?

Sun Apr 24, 2011 4:27 pm

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.

derkraut
Posts: 1516
Joined: Fri Jul 16, 2010 7:39 pm
Delivery Date: 14 Jun 2011
Leaf Number: 004248
Location: San Diego vicinity

Re: Revised gearing for highway commuters?

Sun Apr 24, 2011 4:38 pm

I would imagine that Nissan tried all the stuff you guys are talking about, when they developed/tested the Leaf. :?:
Derkraut
Color: Cayenne SLE, ETEC trim
reserved: 5/15/2010
Leaf del. 6/14/2011
New Traction battery installed on 7/28/2017:

Return to “Engineering”