Subaru AWD system
Mathieu Lalande
Can someone explain to me (in good details) how the AWD system of the
Impreza works ?
Is it a 50/50 system, or front wheel drive and if you loose traction the
system will deliver power to the back wheels, is it an axl to axl system or
can the power be distributed to the wheels of the same side ???
Thank !!!!!!!!!!!
Math
ma...@sw.ca
jetfreak
the rear. As slippage occurs, the car's computer will transfer more torque
to the axle that requires it. In manual models, the split is 50/50. This
system utilizes a central viscous coupling to transfer power to the axles.
Again, each axle that needs power, gets it automatically. Try this link.
www.subaru.com/awd/inside_fr.html
J
"Mathieu Lalande" <ma...@sw.ca> wrote in message
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smashpdx
have a limited slip or standard (open) diff.
First, the front-to-rear question:
If you have a manual tranny, torque is provided 50/50 front/rear via a
viscous coupling acting as the center diff. If a wheel breaks loose,
its driveaxle spins faster, the VC fluid heats up, gums up the works,
and brings the front and rear driveaxles closer into line with each
other speedwise.
If you have an autotranny, torque is normally split 90/10 front/rear
via the electronically controlled tranny. In the event of slippage the
spin-up of one drive axle vs the other is detected and power is
electronically transferred from front to rear as needed. I think it
will top out at a 50/50 split. Also, 1st and 2nd gear, unlike 3rd and
4th gears, are normally split at 50/50 regardless of conditions.
The one glaring exception to this is the new Outback with the H6 engine
and VDC (not the LL Bean-- it doesn't have VDC), and in that case the
default split is 45/55 front/rear.
Now the side-to-side question:
Most Subarus ship with a standard, or "open" differential. In such a
differential, if one wheel has traction while the other has broken
loose, the loose one will spin endlessly while more and more power is
applied via the driveaxle. On a vehicle with four wheels and two
axles, this is OK if only one wheel has broken loose. But if you have
two wheels break loose-- one on each axle-- you're pretty much sunk
from an AWD standpoint. Since the diff is an open one, there's no way
to transfer power "side to side," and since both axles are spinning out
of control, there's no front-vs-rear variation for the system to pick
up on (manual or electronic) to even *attempt* to do anything about
(and even if it could, hey, the wheels are spinning because the diffs
are open, so you're still sunk).
If your Subie has a limited-slip or Torsen diff, or has been equipped
with diff locks (not exactly a dealer-installed option), you can
eliminate the left-right spin to a point where you can transfer some
power to the non-spinning wheel and dig yourself out. However, these
are nonstandard options.
If you have one of the new H6 VDC Outbacks, you get a prettier
scenario: the VDC system will detect wheel spin and apply braking
action to the wheel in question. This in combination with the stock
AWD system and some additional VDc-specific tweaks can effectively
cause power to be transferred "from the side that slips to the side
that grips."
Maybe that was a little bit more than you asked for but I hope it's
comprehensive. Others can feel free to jump in if I missed something
or got it wrong, I'm still getting comfortable with all this stuff. :)
-Russ
In article <huNZ5.10019$u73.4...@wagner.videotron.net>,
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Eric Lee Green
>Can someone explain to me (in good details) how the AWD system of the
>Impreza works ?
>
>Is it a 50/50 system, or front wheel drive and if you loose traction the
>system will deliver power to the back wheels, is it an axl to axl system or
>can the power be distributed to the wheels of the same side ???
Depends. Manual transmission is 50-50. Automatic transmission is 90-10
front wheel drive and if you loose traction a clutch pack is
electronically engaged to shift power to the back wheels. It is
axle-axle unless you have a limited-slip diff (dunno if any Imprezzas
have one). So yes, without the limited-slip diff, you can have both
right wheels sitting on ice and spinning helplessly while the left
wheels on dry pavement sit like lumps.
--
Eric Lee Green There is No Conspiracy
er...@badtux.org http://www.badtux.org
Mathieu Lalande
Have a good one !
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