what is the best AWD system?

[whitetiger]

the systems in the 6mt wrx sti is the best for most conditions. 3 full LSDs that are either clutch type or torque sensing. these types of diffs respond nearly instantly and need no VDC,ESP, TC, SC or other electronic system to work.

 

viscous diffs are reactive and require slippage to occur in order to generate heat and lock to work.

[rsd220]

i am waiting the answer

[Brady]

Which Subaru AWD system? There have been several. Some of the systems are primarily FWD, and with an open front diff, sure, one wheel could receive all of the torque.

 

It's a silly posit, though, because even a FWD car with an open diff won't ever REALLY send 100% of the torque to one wheel.

[Platinum_Racing]

The only way to send close to 100% of the torque to one individual wheel is if you have a 2WD car with an open diff, and you're stuck in something heavy like snow or mud. Whenever one wheel has significantly more traction than the other a 2WD car with an open diff will send MOST of the torque to one wheel, but that isn't a good thing. That only ever happens if one wheel is getting traction and the other isn't. In an open diff, torque will follow the path of least resistance, usually AVOIDING the wheel with the most traction in favor of the wheel which is easiest to turn.

 

In early AWD Subaru systems it is possible to replicate this by installing the "FWD Fuse" under the hood, but other than that no, a Subaru will never send 100% of its torque to one wheel. The center differential will always compensate. Unless you put those wheel locks they use in Japan on 3 out of the 4 wheels, the center diff will always try and compensate, but if you tried this you'd certainly break something.

 

Why would you ever want to send 100% of the power to one wheel anyway? If you have an old Subaru (First or Second gen Legacy for example) install the "FWD Fuse" and find a 2' deep mud pit. That's the closest you'll ever get to achieving 100% torque to one wheel.

[MikeNH]

I think you're all looking at this backwards- suppose three wheels are on a low/no grip surface like ice and one tire is on a solid surface like tar or dirt. Could that one wheel pull the car free?

[mwiener2]

With the 5EAT and VTD the car can use the brakes to send power to a single wheel. It won't be 100%, but it will be more than the other 3 wheels. It's only meant to work for very short bursts at a time.... no rock crawling

[Platinum_Racing]

At most the torque distribution to one wheel will probably only be 50-60%. That would leave the other three wheels with 10-12% torque a piece.

 

Three wheels on ice, one on dry pavement. With the 5EAT's and the VTD mweiner mentioned, the diffs will transmit more power to the one wheel with traction by using the brakes to slow the slipping wheels. With older, simpler Subaru AWD platforms, the three wheels will slip and the center differential will change from a 90/10% front/rear torque bias to a 50/50% front/rear torque bias. From there if the car has open diffs the wheel with traction won't get nearly as much power as the wheel without traction. If the car has LSD's the front or rear differential (Whichever is responsible for the slipping wheel, but I don't think Subaru had LSD's on the front wheels back then) will try and even out the torque distribution as much as possible, up to 50/50% of the torque the differential receives from the center diff. Even in the most ideal conditions, each wheel would still only get 25% of the total torque of the engine.

[Platinum_Racing]

http://i338.photobucket.com/albums/n415/Wargrimes88/2009_subaru_legacy-pic-34263.jpg

 

http://i338.photobucket.com/albums/n415/Wargrimes88/2009_subaru_legacy-pic-34263-Copy2.jpg

 

http://i338.photobucket.com/albums/n415/Wargrimes88/2009_subaru_legacy-pic-34263-Copy.jpg

 

http://i338.photobucket.com/albums/n415/Wargrimes88/Lowtracnolsd.jpg

 

It took me a couple minutes to make these, but I hope these pictures give you a visual of what I'm talking about.

 

 

 

I'll let someone who knows more about newer Legacy's explain how that works, but like mweiner said, the system provides more precise control over which wheel gets traction by using the brakes to slow individual wheels. This sends more power to the remaining wheels. More than that I can't help you since I don't own one. I don't want to tell you the wrong thing and get flamed off Earth.

 

Also, I get the feeling we're helping someone win some sort of a bet, seeing as how you joined just to ask us this question. Good luck, I guess.

[ehsnils]

And don't forget that there is a difference between 5MT and 4EAT gearboxes - they have a different center solution. Pics above describes the 4EAT solution - which is the only variant where the AWD disable fuse works.

 

And you also have this thread: http://legacygt.com/forums/showthread.php/best-awd-systemi-144893.html?t=144893 , same basic subject.

[rsd220]

this is information about saab xwd system

http://www.autoblog.com/2007/11/30/saab-xwd-haldex-4-0-all-wheel-drive-system-up-close/

 

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

 

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 ?

 

see XWD can send 85% of torque to one wheel

http://www.trollhattansaab.net/wp-content/uploads/2007/07/haldexxwd1.jpg

[ehsnils]

Merged threads - no need to create new threads on the same subject.

[rao]

Merged threads - no need to create new threads on the same subject.

 

So that is why there is only one oil thread

 

Subaru's AWD system is superior to all others

 

/thread.

[rsd220]

ok

in old subaru maximum torque distribution on front wheel is 45% and rear wheel is 30% Is it right ?

 

what about subaru legacy 2010 2.5i Lineartronic ™ CVT

 

which type it has of SYMMETRICAL AWD ? continuous,active or VTD

 

very thanks for all members that help me

 

[rsd220]

for Symmetrical AWD, it actively distributes engine torque to individual wheels

http://www.subaru-global.com/awd_torque.html

[mwiener2]

in old subaru maximum torque distribution on front wheel is 45% and rear wheel is 30% Is it right ?

 

 

and the other 25% goes right out the window

 

 

all Subaru AWD systems are symmetrical

 

and it's wonderful that you figured out how to use bold and colors and what not... but you're not gonna get positive attention from using it

[rsd220]

[ame=http://www.youtube.com/watch?v=6xhf81kCjlo&p=7164A6815D8EFB42&index=4]YouTube - Saab XWD[/ame]

[Platinum_Racing]

Now that we know you're talking about a new Subaru, lets see if we can help you.....

 

 

 

 

 

You step on the skinny pedal...

 

The computer gives you traction.

 

/thread

[ehsnils]

If you compare the Haldex with the Subaru AWD you first have to consider that the Haldex is a reactive system that engages the rear axle only when there is a slippage. Before that you have almost all traction on the front axle. Only the Subaru 4EAT has a system that is similar to the Haldex but it doesn't work the same way.

 

The other versions of the Subaru AWD works with a permanent center differential. The center differential have different gearings depending on the type of gearbox and different type of LSD functionality. The 5MT has a viscous coupling while the 5EAT has a computer controlled LSD clutch pack and the 6MT with DCCD has a computer controlled clutch pack with manual override option.

 

The CVT has a system similar to the 4EAT.

 

But then - the mechanics of the AWD system is only one factor, another factor is also important - when you have a computer controlled system - how is the algorithm for engaging the LSD designed? It's also important, and the only way to really decide which system that is better than another is to compare the cars on a test track. And on the test track use the various conditions for which you plan to use the car. (Towing, Loaded car, no load and of course driving style)

 

In most tests done by car magazines comparing with other cars the Subaru systems seems to do well. So I suggest a search on the net for car tests where Subarus are involved.

 

And another factor - if you have an even distribution of torque between front and rear you will keep down the tire wear, which systems like the Haldex system don't.

[rsd220]

ok

Under normal conditions the car will send power like this:

Front Left - 25%

Front Right - 25%

Rear Left - 25%

Rear Right - 25%

 

but in specific condition if front right wheel is slip

how is torque distribution on all wheels?

Front Left -? %

Front Right ? %

Rear Left -? %

Rear Right - ? %

 

but in specific condition if rear lift wheel is slip

how is torque distribution on all wheels?

Front Left -? %

Front Right ? %

Rear Left -? %

Rear Right - ? %

[rsd220]

the Haldex is a reactive system that engages the rear axle only when there is a slippage. Before that you have almost all traction on the front axle

yes but this is on old generation but new generation Haldex IV is different

 

read this please

Fourth generation - 2007

 

Saab introduced a unique combination of Haldex Couplings on its 9-3 Turbo-X in late 2007. Called XWD (Cross-Wheel Drive), it allowed enhanced traction, safer driving, and better control. The main components of the new Haldex system are the Power Take-Off Unit (PTU), Limited Slip Coupling (LSC) and eLSD (Electronic Limited Slip Differential). The PTU is the final drive unit at the front of the vehicle that transmits power to the front wheels and sends power down the driveshaft to the rear wheels. It is not a Haldex design, but is required to adapt the system to a front-wheel drive vehicle. The LSC sits at the rear of the vehicle in-line with the driveshaft. It controls the torque split between the front and rear wheels of the vehicle. The LSC sends torque to the eLSD that sits between the rear wheels. The eLSD transfers torque to the two rear wheels. Like with XWD, previous generation Haldex systems also included an LSC and an LSD. However, with the new system Haldex significantly redesigned the workings of their LSC. The LSC is still a clutch pack that adjusts torque split depending on hydraulic pressure. It is the method of fluid flow through the device that has changed.

 

A large complaint about the old system was its lagging response time. LSC versions 3.0 and earlier used a built-in pump to create hydraulic pressure on the clutch pack to increase the torque drive to the rear wheels. While efforts were made on Haldex's part to create pre-emptive torque by adding a check valve and feeder pump to provide some instant pressure when triggered by wheel slippage, it was still limited in capacity. That is why for version 4.0 Haldex made an effort to improve response time by eliminating the hydraulic pump built in to the LSC, which also reduced its overall packaging size. Instead they have added a proportional pressure release valve with an accumulator that is kept filled by a detached feeder pump. This provides more instant response by holding the valve open to limit the torque drive to the rear wheels and keeping the hydraulic fluid flowing through the system. That way when rear torque is demanded, the valve closes and hydraulic pressure is already there.

 

The LSD used by Haldex 4.0 is also not the mechanical limited-slip differential of old. They swapped the old system LSD for an electronic unit. The eLSD works in much the same way as the LSC, a feeder pump and pressure relief valve are used to control hydraulic pressure on the differential clutch pack. This allows for complete control of the rear differential lock-up without the need to wait for wheel slippage to occur. The system has its own control unit contained in the LSC. This control unit communicates between the vehicle systems to get sensor input for data such as wheel speed, rpms, throttle position, steering wheel input, etc. It also works with anti-lock brake and traction control systems.

 

The XWD system can transmit 100 percent of available torque to either the front or rear wheels. However, for those conditions to occur one end of the vehicle would have to lose all traction, like driving on ice for instance. During a standing start the rear wheels are put to use, without the need for any slip to occur. Then under straight-line cruising conditions, to conserve fuel and driveline wear, the torque split to the rear wheels is reduced to a level between 5 and 10 percent. Also up to 85 percent of torque can be transferred by the eLSD between to any single rear wheel if necessary. The system can adjust torque splits based on calculated conditions, such as those that indicate an aggressive lane change manoeuvre, to effectively reduce oversteer or understeer without any wheel slip occurring. In the event that some wheel slip does actually get to occur, the system can react more timely and efficiently than in the past.

 

Thanks to this technology, the Saab 9-3 Turbo-X, with only 280 bhp (210 kW) can run a slalom faster than many high performance sports cars, beating German and Japanese rivals. Saab has an agreement with Haldex for exclusive first year access to the technology, and use of the "XWD" trademark. Haldex is currently developing a similar AWD system for Hyundai Applications.

[fishbone]

No thanks. Sounds like they shoved a bunch of electronic nannies to improve something a good old system can do it in a mechanical form. I'd also like to know how reliable, dependable that system is. Or, failing that, how much it costs to fix it ...

That's one thing many people forget when talking Subaru AWD. The whole point behind it is to work great for cheap and simple.

[wpgspecb]

lolz @ 1:41....

 

the car model in the upper right does NOTHING in this video, kinda a waste of time..

 

 

fwiw, my friend had a 2005 wrx stage2 with no TC or VDC etc etc. and traded for a 2010 Audi A3, with the aforementioned haldex controlled awd. He was not told of this audi "quattro" not being full time all wheel drive. While he loves the car, he hates the fact that his wrx was better in almost every way.

 

The only 2 Audi Quattro models that arent All-Wheel Drive are the A3 and TT, fyi.

 

Quattro no longer means, ft-awd.

 

If you google search for haldex bypasses, you can buy a ecu addon that FORCES awd 100% of the time and even allows you to control torque distribution. The downside to this is you are running essentially a 4WD car, with FWD bias, in AWD mode, 100% of the time, adding strain and stress to a drive-train and transmission that was not engineered to handle FT-AWD.

[ehsnils]

The only Quattro worth it's name is the original one with a torsen center diff.

[fishbone]

I agree

[praedet]

No thanks. Sounds like they shoved a bunch of electronic nannies to improve something a good old system can do it in a mechanical form. I'd also like to know how reliable, dependable that system is. Or, failing that, how much it costs to fix it ...

That's one thing many people forget when talking Subaru AWD. The whole point behind it is to work great for cheap and simple.

Well, I do like the current STi's set-up, and that has the e-nannies

 

If it had some of the abilities it has had in other countries in the past, like the yaw sensors, that would be even better...