HOW MUCH MAXIMUM OF TORQUE DISTRIBUTION SEND TO ONE WHEEL ON

[rsd220]

HOW MUCH MAXIMUM OF TORQUE DISTRIBUTION SEND TO ONE WHEEL ON LEGACY CVT 2.5I 2010 ?

i know Subaru AWD in normal condition torque distribution 50/50
but in specific condition how much maximum of torque can send to one wheel front or rear ?

see XWD can send 85% of torque to one wheel
http://www.trollhattansaab.net/wp-content/uploads/2007/07/haldexxwd1.jpg

[TheAngryPidgeon]

Actually, with the CVT, it's closer to 55/45 F/R. But I don't know the maximum to a single wheel. The conditions necessary to elicit such a torque distribution would be so abnormal that it is almost irrelevant.

[Huffer]

Buy a motorcycle.

But seriously, you'd need to have a diffs capable of this. The closest thing i can think of is the Mitsi Evo or the Acura SH-AWD systems.

This would take a lot of work to retrofit to a Subaru.

[98outbackpdx]

the SAAB XWD system in the saab 9-3 has this system

[TheAngryPidgeon]

Realistically, if you have 3 wheels slipping to the point of getting you to 85% torque at one wheel, you have bigger issues that what a single wheel can max out at. The most probable of these issues would be the spin you're about to go into.

[jey]

Subarus can send almost 100% of the torque to one wheel under certain circumstances. But the key here is WHICH wheel, which is demonstrated in the original diagram.

I can think of many situations where it'd be nice to have 85% of the torque going to the correct wheel - say you're stuck in some snow or mud and only one wheel has traction.

And Subaru DOES have a system like XWD, if you have VCD (which I believe all US Subarus have now.) VCD will apply brakes to the spinning wheel so more of the torque gets transferred to the wheel with traction. There is a Subaru promotional video showing this real life situation and it distributed a LOT of the torque to the correct wheel - it would not surprise me if it was close to or exceeding 85%. It's pretty much the same system as XWD (applies brakes to the slipping wheels.)

http://www.youtube.com/watch?v=ooQRxlChvMw

Fast forward to 7:50 for the demonstration of the Subaru Legacy with VCD, the 3 wheels on ice.

Fancy diffs are the traditional/better way of doing this, which the STi and EVO have. Nowadays they just use the brakes to do this on most cars :(

[TheAngryPidgeon]

You can see the other wheels spinning like crazy though, even as the VDC engages the wheel with traction. So it really is nowhere near 100% to that single wheel.

[jey]

I would say spinning about 7 rotations is hardly "like crazy". Yes, it does have to spin SOME because that is the only way the AWD system can ever tell there is no traction on that wheel. This is going to be true of every AWD system. But once the lack of traction is detected clearly most of the torque is directed properly. Spinning like crazy would be like the VW at 6:10 on that video...

[ouch1011]

The older non-sti Subaru AWDs are capable of sending pretty much 100% power to 1 wheel under certain conditions. If you lift 1 tire completely off the ground (or if that 1 tire loses traction almost completely, as in winter conditions) all the power will go to that 1 wheel. The center VLSD will attempt to distribute power to the wheels axle opposite the spinning tire but if there is enough of a difference in traction, it will overpower the VLSD and send nearly all the power to the 1 spinning wheel. Applying brakes to the spinning tire (as most modern traction control systems do) helps with this alot because it simulates traction on that wheel.

I don't know this for sure, but I believe systems like the Honda SH-AWD system use the brakes to specific wheels to direct power specifically. I think its only real differentiation is that it "applies power" to the outside wheels on a turn to help steer through the corner. This could also be accomplished by braking the inside wheel. Again, I don't know this for sure, I'm just thinking of the most simplistic method to get their described results.

[jey]

I don't know this for sure, but I believe systems like the Honda SH-AWD system use the brakes to specific wheels to direct power specifically. I think its only real differentiation is that it "applies power" to the outside wheels on a turn to help steer through the corner. This could also be accomplished by braking the inside wheel. Again, I don't know this for sure, I'm just thinking of the most simplistic method to get their described results.

Right, using braking to direct power is the most simple and common technique used by most systems now, but interestingly enough SH-AWD is actually more advanced. The rear axles have planetary gears controlled by electromagnetic clutch packs to direct power left/right, which actually also acts to direct power front/rear since there is no center differential.

[TGX4776]

the SAAB XWD system in the saab 9-3 has this system


It's also in the new 9-5 and may be in the new 9-4x SUV


It's a pretty sweet system actually. I got to test it out when my C900 went in to get a new fuel pump and it just happened to coincide with a nasty icy snow storm. Passed more then a few stuck SUV's. I'll have to compare it to my AWD in the leggy this winter if it snows here.


It was a loaner BTW. A brand new car and I was the first person to drive it. A Saab would be the only car I would buy new.