I'll take a stab at this but won't guarantee 100% accuracy...
First the basics, as I know them, of an open-differential. Power follows the
path of least resistance and only that amount of power provided to the wheel
easiest to spin goes to the other wheel. For example, if one wheel is on ice,
only the amount of power required to spin that wheel (the one on the ice) is
transferred to the opposite wheel. This is why you get stuck even though one
wheel has good traction under it.
In our AWD (full-time 4wd), I am told there is an open-diff. type mechanism in
the transfer case which is what allows the vehicle to be driven on dry paved
roads (high traction conditions) without binding. Therefore (keep in mind that
this is the part that I can't guarantee 100%) and in theory, if you get the back
wheels spinning only a minimal amount of power will be transferred to the front
axle.
With all of this said, I gotta tell you that in practical, real world
applications, I've never gotten stuck nor sensed any loss of "pulling power"
when I've been in full-time 4wd (AWD) mode --In other word, I love it! On the
other hand, when I've been doing serious off-roading, I always use the part-time
4wd mode where power is provided by some ratio (40% front:60% rear?) to each
axle.
You've kinda piqued my interest and I'm almost tempted to back the rear wheels
onto a frozen lake somewhere and see if the front wheels will pull me out in
"AWD" mode... Unfortunately, I don't have a frozen lake handy so I doubt I'll
be doing this anytime soon. Moreover, I've got a locker in the rear diff. so
the equation is probably a little different for me... ;-)
Tom
____________________Reply Separator____________________
Subject: Re:DML: Transfer Case Options
Author: <dakota-truck@buffnet.net>
Date: 3/1/2002 10:39 AM
Ok, still trying to find the answer for this with our AWD systems:
In high traction conditions (paved roads), which wheel(s) is getting 100%
of the torque? There is no full time torque split, right?
Thanks...
On Fri, 1 Mar 2002 fawcett@uism.bu.edu wrote:
> JP,
>
> I agree completely with your observations and I got the "Full-Time" 4wd option
> in my Kota for much the same reason as you.
>
> Just one minor thought/clarification though, the AWD system in the current
> Kota's differs markedly from a part-time system in that there is a "center"
> open-differential (between the front and rear axles) which allows this system
to
> be operated in high traction conditions (paved roads). In theory this does
make
> the system less "aggressive" for extreme wheeling due to power distribution
> concerns inherent in any "open differential" design.
>
> For me, I've got the best of both worlds in that my '98 has both a part-time
and
> full-time (in addition to part-time 4lo) position on the shifter... Hooray
for
> me! ;-)
> Tom
>
> ____________________Reply Separator____________________
> Subject: DML: Transfer Case Options
> Author: <dakota-truck@buffnet.net>
> Date: 2/28/2002 8:35 PM
>
> This is a bit of a test since I just joined the DML. I own an '01 CC 4.7
> SLT+ AWD ABS LSD. I also own a '99 Jeep GC with the Quad Drive and Subaru
> Legacy with it's AWD system. As you can see I am a believer in AWD. Not so
> much from the off road capability but from the safety and performance
> standpoint. In the pacific northwest we have a wide variety of road
> conditions that can change rapidly. I have been generally pleased with the
> AWD vehicles that I have and they track well whether I hit large puddles on
> the highway or head over on of the many Cascade passes with snow and ice. I
> consider the capability much like insurance. You are paying extra until you
> really need it. With respect to the thread about Transfer Cases I have to
> say I am very pleased with the Dakota version. In AWD mode it is just an
> open differential (in function) in the TC but the performance is great on the
> hiway. Bonus, I can do full throttle launches with the 4.7 and ALL power
> goes to motion rather than smoke. As others have indicated, all the parts
> are in motion whether you have part-time or AWD. My on hiway fuel economy is
> 20+ around town is 16+...........unless I start having fun. I have had other
> pickups with part time systems and so far this is far and away the best. My
> advice with many years experience with various 4 wheel drive systems is get
> the AWD.
>
> JP
>
>
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