Go Back   EcoModder Forum > EcoModding > EcoModding Central
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 10-29-2009, 11:40 PM   #21 (permalink)
Master EcoModder
 
roflwaffle's Avatar
 
Join Date: Dec 2007
Location: Southern California
Posts: 1,489

Camryaro - '92 Toyota Camry LE V6
90 day: 31.12 mpg (US)

Red - '00 Honda Insight

Prius - '05 Toyota Prius

3 - '18 Tesla Model 3
90 day: 152.47 mpg (US)
Thanks: 348
Thanked 120 Times in 79 Posts
Quote:
Originally Posted by Frank Lee View Post
Back in the day I read a comment from an Audi engineer saying the AWD doesn't hurt fe because a powered wheel has less rolling resistance than an unpowered wheel and that pretty much cancelled out the extra weight and mechanical transmission losses. They made it sound like an fe wash.
How does that work? I could buy a negligible difference, since a decent axle is at what, ~97-99% efficiency, and an extra ~50lbs won't do much, but I've never heard of a powered wheel having less RR.

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 10-29-2009, 11:47 PM   #22 (permalink)
(:
 
Frank Lee's Avatar
 
Join Date: Jan 2008
Location: up north
Posts: 12,596

Blue - '93 Ford Tempo
Last 3: 27.29 mpg (US)

F150 - '94 Ford F150 XLT 4x4
90 day: 18.5 mpg (US)

Sport Coupe - '92 Ford Tempo GL
Last 3: 69.62 mpg (US)

ShWing! - '82 honda gold wing Interstate
90 day: 33.65 mpg (US)

Moon Unit - '98 Mercury Sable LX Wagon
90 day: 21.24 mpg (US)
Thanks: 1,534
Thanked 3,383 Times in 2,128 Posts
I don't know how that works. That's what the dude said, back in the '80s and he didn't expound on it IIRC.

Quote:
During testing, Audi also found another benefit: tyres generate less rolling resistance when driven gently than when rolling freely, more than enough to offset the additional frictional losses in the four-wheel-drive transmission. Prototypes delivered higher maximum speeds when driven by all four wheels than when the rear driveshafts were removed.
http://www.pistonheads.com/doc.asp?c=52&i=10065

Ahhh- here we are:

http://books.google.com/books?id=Ldk...stance&f=false
__________________



Last edited by Frank Lee; 10-29-2009 at 11:53 PM..
  Reply With Quote
Old 10-30-2009, 12:26 AM   #23 (permalink)
Master EcoModder
 
roflwaffle's Avatar
 
Join Date: Dec 2007
Location: Southern California
Posts: 1,489

Camryaro - '92 Toyota Camry LE V6
90 day: 31.12 mpg (US)

Red - '00 Honda Insight

Prius - '05 Toyota Prius

3 - '18 Tesla Model 3
90 day: 152.47 mpg (US)
Thanks: 348
Thanked 120 Times in 79 Posts
The only thing I can come up with is that by spitting power between two axles the axle losses are minimized over some operating range, so it may look like having a driven wheel minimizes RR, but in fact it's that axle efficiency isn't linear and can be optimized to some extent.

Edit- Jeez , I've had five beers and I'm talking about axle losses. I should just get a degree in ME and call it a day.
  Reply With Quote
Old 04-01-2010, 09:11 PM   #24 (permalink)
EcoModding Lurker
 
Join Date: Apr 2010
Location: colorado
Posts: 1
Thanks: 0
Thanked 0 Times in 0 Posts
awd and hypermiling the redneck way

One thing that hypermiling can gain is eco friendly good habits but when you are picking a car to set up hypermiling it may be best to look at all of the aspects first , and dont fall into the old trap that any body can hypermile with any car , for example if you have a big van you may sacrifice any fuel gain due to the shear size of the vehicle . awd is also a factor in picking a vehicle as well ,why ? well take for example a subaru the awd is mounted in the rear and is always turning while the car is moving , the separation point is in the transfer case so that means that everything up to that point is turning , redneck thinking is this way k.i.s.s. keep it simple stupid (not calling anyone stupid) but by looking at all the factors of saving gas or diesel all factors are concidered, think of it this way..... can you get out and push your car down the street a ways? i know for a fact that a subaru is a tough push for one person , that said now you know the engine will still work hard even cruseing . so what im saying is that hypermiling can work but if you really want it than you have to think outside the box and disregard some of the rules . more later
  Reply With Quote
Old 04-02-2010, 12:53 AM   #25 (permalink)
Banned
 
Join Date: Feb 2008
Location: maine
Posts: 758

oldscoob - '87 subaru wagon gl/dr
90 day: 47.06 mpg (US)
Thanks: 21
Thanked 18 Times in 14 Posts
I run AWD.. with a 3 main boxer. 90hp.
3 modes to transmission..
4wd hi == lsd rear,
4wd lo == full diff lock, and reduction
2wd == open front, no rear.

no difference at all bewteen 4hi and 2wd in gas consumption.
could stay there all day...in maine, I have many days.
there is even a momentum, after speed achieved..and no difference in throttle getting to a speed...but once at speed, it seems as though, I am even less toes on the throttle..a momentum is happening in the 4wd. I did learn this similar drivetrain from an inline four, and it was not the same.

But inline fours are notorious for completely dying to the word called "work", there is no torque, until it gets over itself. the boxer is just simply there at all times...every single last rpm...all the way to bogging like a diesel, and still keeps going.

vw AWD synchro van, and old subarus...similar results.
  Reply With Quote
Old 04-02-2010, 01:54 PM   #26 (permalink)
Master EcoModder
 
Join Date: Feb 2009
Location: Phoenix
Posts: 595
Thanks: 106
Thanked 113 Times in 71 Posts
Extra weight is extra weight, and extra spinning weight is extra spinning weight.


I'd be surprised if there was any consistent difference in mpg whatsoever between an AWD car in AWD mode and an AWD car with all of its drivetrain bits spinning but only 2 wheels actually receiving torque from the engine. The wheels don't care if they are connected to the engine by a shaft or by a planet whose surface links the front wheels to the rear, the net result is the same parts spinning and causing drag.

As a side note, early (at least through 2001) 5-speed Foresters (and probably other soobs) directly transmit engine torque to the front wheels and only utilize their viscous coupling to link the front wheels to the rear. What this means is on those vehicles you can simply unbolt the rear diff & drive shafts and remove them entirely from the vehicle with no consequence other than loss of AWD. The output yoke on the transmission will just spin and the front wheels will continue to receive 100% engine torque.
__________________
2005 Escape 2.3 MT 2WD
2002 Mustang 3.8 AT
2015 Ram 1500 5.7L 4WD
2002 Motobecane 700DS
  Reply With Quote
Old 04-02-2010, 03:11 PM   #27 (permalink)
Master EcoModder
 
AeroModder's Avatar
 
Join Date: Jan 2010
Location: Oregon
Posts: 471

Tank - '96 Ford Aspire 4 door
Team Ford
90 day: 46.75 mpg (US)
Thanks: 15
Thanked 65 Times in 48 Posts
In Subarus, cars with automatics have a 90/10 torque split while cruising to offset the dragging of the rear wheels (electronically controlled transmission control unit), but the manual models have a 50/50 (Center differential with a viscous coupling device).

Subaru's All Wheel Drive System - AutoWorld.Com

I was actually thinking about looking for an Impreza for my next project, since there's so many more aftermarket parts out there than there are for Tempos.
__________________
In Reason we Trust
  Reply With Quote
Old 04-02-2010, 05:51 PM   #28 (permalink)
EcoModding Lurker
 
Mifunego's Avatar
 
Join Date: Nov 2009
Location: The People's Republic of Chicago
Posts: 69

The Taco - '99 Toyota Tacoma Prerunner
90 day: 19.29 mpg (US)
Thanks: 5
Thanked 13 Times in 9 Posts
Quote:
Originally Posted by Frank Lee View Post
I don't know how that works. That's what the dude said, back in the '80s and he didn't expound on it IIRC.


Audi quattro

Ahhh- here we are:

Popular Mechanics - Google Books
Sounds interesting, but I'm not familiar with any Audis that can flesh out that theory in terms of FE, at least according to the EPA (and my limited VAG experience). Of the models that I'm familiar with, available both in FWD and quattro (or haldex), the FWD always is rated at a better mpg. Maybe that wasn't the case with the early 80's models? Go figure.

Last edited by Mifunego; 04-02-2010 at 05:54 PM.. Reason: fun
  Reply With Quote
Old 04-02-2010, 06:24 PM   #29 (permalink)
Master EcoModder
 
Join Date: Feb 2009
Location: Phoenix
Posts: 595
Thanks: 106
Thanked 113 Times in 71 Posts
Quote:
Originally Posted by AeroModder View Post
In Subarus, cars with automatics have a 90/10 torque split while cruising to offset the dragging of the rear wheels (electronically controlled transmission control unit), but the manual models have a 50/50 (Center differential with a viscous coupling device).

Subaru's All Wheel Drive System - AutoWorld.Com

I owned an 01 Forester with manual transmission and personally had it apart. The engine (through the transmission) drives the ring gear of the front wheels directly and a jack shaft drives the rear output flange to the rear axle through the viscous coupling. When I disconnected the rear driveshaft and attempted to verify this by crawling up a curb, and by dumping the clutch on flat dry pavement, it behaved like a front wheel drive car with 100% engagement.

Hypothetically if you removed the front axle shafts from the same vehicle and tried to drive it as a rear wheel drive, it would only be able to deliver half of its torque to the drive axle and would likely wear itself out by freewheeling the front flanges any time the engine supplied more torque than the coupling wanted to send the rear wheels (such as acceleration/climbing/etc)
__________________
2005 Escape 2.3 MT 2WD
2002 Mustang 3.8 AT
2015 Ram 1500 5.7L 4WD
2002 Motobecane 700DS
  Reply With Quote
Old 04-02-2010, 06:25 PM   #30 (permalink)
EcoModding Apprentice
 
micondie's Avatar
 
Join Date: Mar 2009
Location: Western Mass
Posts: 104

moby van - '03 Dodge Caravan SE
90 day: 19.74 mpg (US)
Thanks: 0
Thanked 5 Times in 5 Posts
I remember reading years ago about an AWD Can-Am race car that somebody was building and their conclusion was that since frictional losses were a percentage of the power being transmitted, splitting the power between the front and back axles cut the losses to each axle in half resulting in the total losses being about the same. This would explain why cutting power to the rear axle in an AWD vehicle but retaining all the moving driveline parts would reduce MPG because you would be using just as much power to move the vehicle and extra power to turn the extra driveline parts. A vehicle with locking hubs such as the Suizuki would be able to eliminate the movement of these parts and show some improvement.

  Reply With Quote
Reply  Post New Thread


Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Winter cold start & idling warm-up experiment MetroMPG Hypermiling / EcoDriver's Ed 17 12-17-2010 04:39 PM
Full size to mini frig experiment Cd Saving@Home 7 10-16-2009 04:56 PM
High MPG Winter Car - AWD? - $4K or less pint EcoModding Central 12 09-24-2009 10:55 PM
Field Weakening Experiment for Speed Increase TomEV Fossil Fuel Free 12 04-10-2008 04:53 PM
Engine-off experiment mattW Hypermiling / EcoDriver's Ed 8 02-18-2008 01:57 AM



Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2019, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com