Somebody explain: Saab XWD vs Acura

[Saaby]

I was just reading up a little on the Saab Turbo X (Don't get me wrong, I'm as big a fan as anybody else here, I've just been way way behind on current events for awhile now. Saab-wise and other wise) and I have a question.

Supposedly the XWD system is revolutionary because it can pass power left to right as well as front to back, but I thought Acura has been doing this for awhile now with their SH-AWD.

Anybody care to explain the differences, and advantages of the Saab system, not just vs. a traditoinal AWD system, but specifically in comparison to Acrua's?

[boon94]

Both systems accomplish the exact same thing, for some reason people think that Sh-AWD can also split torque independantly between the front wheels, however it cannot (same as xwd).

SH-AWD uses twin cluches in the rear differential to distrubite between front back torque, as well as rear left/right torque

XWD uses a torque distributor to seperate front and rear (called a TTD?), and a seperate (eLSD) unit to distribute between right and left on the rear wheels.

Both systems are capable of the same thing. Which one has the better Computer Controller? Which one has the ability to respond faster and more effectively? supposably the XWD unit

Oh Forgot to mention, SH-AWD can only set a maximum of 70% torque to one rear wheel, while XWD can send 85%


Hondas Video
http://world.honda.com/HDTV/news/2004-4040401a/

XWD video
http://www.haldex-xwd.com/

[ACBarnett]

don't forget that mitsubishi has had a similar system in the evo for a few years, and I think nissan has offered something similar in some of the skylines as well

Honda's setup is much more complex than XWD, the clutchpacks scream "wear part" and will surely get expensive to replace later on. On the flipside I think it's a bit lighter than XWD and it's probably a more advanced setup mechanically speaking. All the eLSD is is another haldex wet clutch hooked up to one of the output shafts of the diff.

[queryanalyzer]

Thanks for that. That was informative

I didnt know about Haldex's use in TT and Volvo.

[SaabKen]

Originally Posted by ACBarnett

don't forget that mitsubishi has had a similar system in the evo for a few years, and I think nissan has offered something similar in some of the skylines as well

Honda's setup is much more complex than XWD, the clutchpacks scream "wear part" and will surely get expensive to replace later on. On the flipside I think it's a bit lighter than XWD and it's probably a more advanced setup mechanically speaking. All the eLSD is is another haldex wet clutch hooked up to one of the output shafts of the diff.

It's all here

http://en.wikipedia.org/wiki/SH-AWD

http://en.wikipedia.org/wiki/Haldex

[TooMany2cvs]

Originally Posted by queryanalyzer

I didnt know about Haldex's use in TT and Volvo.

AIUI, the Haldex system Saab are using is the first live implementation of a new generation, so it's theoretically that bit better than existing Haldex systems.

[Mattlach]

An interesting thing about the TTD system in the Turbo X, is that it senses when you are undergoing hard acceleration (kick-down?), and immediately shifts torque to the rear wheels.

If I am not mistaken, other systems like it, (including Sh-Awd) wait for wheel slip, and then compensate, causing significant lag.

[Saaby]

Ok, so the setup itself isn't totally new, but the way they're controlling it is smartest of all.

Kind of like how I use a Mac, and Apple don't always invent totally new stuff (Although sometimes they do) but they have a way of taking an existing technology and really improving the heck out of it.

[mulik51]

Isn't the haldex system on S60R supsed to be able to deliver traction even if 3 wheels are on a slippery surface?

KLim

[brunp]

Just curious how this differs from the Audi systems as they claim to have what the new Haldex system will achieve on our Saabs?

Paul

[snowboardin58]

Originally Posted by Saaby

Ok, so the setup itself isn't totally new, but the way they're controlling it is smartest of all.

Kind of like how I use a Mac, and Apple don't always invent totally new stuff (Although sometimes they do) but they have a way of taking an existing technology and really improving the heck out of it.

Sorta. Except in reality, XWD really is the better choice, and the smarter system.

[boon94]

Originally Posted by Saaby

Kind of like how I use a Mac, and Apple don't always invent totally new stuff (Although sometimes they do) but they have a way of taking an existing technology and really improving the heck out of it.

apple is the spawn of satan

Originally Posted by brunp

Just curious how this differs from the Audi systems as they claim to have what the new Haldex system will achieve on our Saabs?

Paul

They use brakes to redistribute power, we use machines that cause less power loss and more performance

[TooMany2cvs]

Originally Posted by mulik51

Isn't the haldex system on S60R supsed to be able to deliver traction even if 3 wheels are on a slippery surface?

Any 4x4 system with diffs which aren't totally open will be able to do that.

If the centre diff's totally open, all you need is to lose traction at one wheel and you're stuffed.

If the centre's locked, then you'd need to lose traction at one wheel each end to be going nowhere.

Lock one end (usually rear - lock the front, and you only go in a straight line...) and you'd need to lose traction on both wheels that end plus one the othe end.

Lock both ends, and as long as one wheel's gripping, you've got traction.

With partial locking, it's just a question of the maximum torque you're going to get to that wheel.

[SaabKen]

Originally Posted by boon94

apple is the spawn of satan

Maybe. But Bill Gates III is the true 666

[Saaby]

Originally Posted by SaabKen

Maybe. But Bill Gates III is the true 666

Ok, sorry I even tried to draw that conclusion. Moving on...

[ACBarnett]

Originally Posted by TooMany2cvs

Any 4x4 system with diffs which aren't totally open will be able to do that.

If the centre diff's totally open, all you need is to lose traction at one wheel and you're stuffed.

If the centre's locked, then you'd need to lose traction at one wheel each end to be going nowhere.

Lock one end (usually rear - lock the front, and you only go in a straight line...) and you'd need to lose traction on both wheels that end plus one the othe end.

Lock both ends, and as long as one wheel's gripping, you've got traction.

With partial locking, it's just a question of the maximum torque you're going to get to that wheel.

The S60R doesn't have a center diff though, it's a haldex car remember, so it has the haldex clutchpacks instead. Having driven one and poured over the description of the Haldex system it has I think the "maintain traction with 3 wheels spinning" spiel has nothing to do with it's awd hardware and everything to do with Volvo's dynamic stability control/4c. It still applies torque through that one wheel with traction, but it's by applying the brakes on the other three.

That's why they come with such huge brakes

My bigger question for xwd is whether it will drive like the S60R with it's 95/5 baseline front/rear torque split, or like a 50/50 Audi or Subaru. The Audi/Subaru style awd systems are incredibly linear in their power delivery, especially when redistributing the torque. The Haldex system on the S60R on the other hand is crude and unpredictable, it will drive like a 300hp fwd car until the front wheels start spinning then all of a sudden it shunts 30-50% of the torque to the rear making it a really easy car to snap oversteer in poor road conditions.

Hopefully the Turbo X drives more like a real Quattro Audi or Subaru and less like the other fwd/awd Haldex cars that are out there.

[boon94]

XWD is supposed to be so fast and smart that you wont even know its working, you'll just think your a driving master

[900t]

Originally Posted by Mattlach

An interesting thing about the TTD system in the Turbo X, is that it senses when you are undergoing hard acceleration (kick-down?), and immediately shifts torque to the rear wheels.

If I am not mistaken, other systems like it, (including Sh-Awd) wait for wheel slip, and then compensate, causing significant lag.

I think SH-AWD is shifting torque splits all over the place all the time, if it waited for wheel slips then it wouldn't really accomplish anything in terms of the "super handling". The point is to over-torque the outer wheels and such to kind of "push" the car around the bend. The differential normally sort of does this naturally but not really (more just changing speeds).

[TooMany2cvs]

Originally Posted by ACBarnett

The S60R doesn't have a center diff though

Of course it does.

, it's a haldex car remember, so it has the haldex clutchpacks instead.

There y'go. That's the diff. It's a clever diff, sure, but it's a diff.

[SaabKen]

Originally Posted by 900t

I think SH-AWD is shifting torque splits all over the place all the time, if it waited for wheel slips then it wouldn't really accomplish anything in terms of the "super handling".

Several 2009 Hondas/Acuras will feature their latest iteration to be called SDH-AWD: "Super Duper Handling AWD"