Haldex = false 4wd?

[sukebe]

Hi guys, I'm a new member here but I've been reading r6.com for awhile now.... someone forwarded me this site last night http://www.rallycars.com/Cars/4wd_turbo_cars.html
and I quoted what's on the site below... it has been bothering me, I love audi's car especially its all wheel drive but from reading this I makes me feel bad... about the all wheel drive being fake, I'm no expert on the system, can someone explain it to me?? Thanks alot.




"Before going further I would like to warn you on some manufacturer's marketing policies. Not all cars advertised as 4 wheel drive are really 4WD. Volkswagen and Audi sell cars advertised as 4WD which, in fact, are not full time 4WD. Cars such as the VW Golf Synchro, 4Motion and Audi A3, S3, TT as well as the Seat Leon (all of which share the same platform and engines) have engine torque sent to the rear wheels only in case front wheel spin is detected. The above mentioned cars use a Haldex type clutch center differential which is only activated when the front wheels spin and always deactivated when braking. If you're in the market for a full time 4WD car you might want to avoid such models and go for the real thing."

[Erik]

Originally posted by sukebe
"Before going further I would like to warn you on some manufacturer's marketing policies. Not all cars advertised as 4 wheel drive are really 4WD. Volkswagen and Audi sell cars advertised as 4WD which, in fact, are not full time 4WD. Cars such as the VW Golf Synchro, 4Motion and Audi A3, S3, TT as well as the Seat Leon (all of which share the same platform and engines) have engine torque sent to the rear wheels only in case front wheel spin is detected. The above mentioned cars use a Haldex type clutch center differential which is only activated when the front wheels spin and always deactivated when braking. If you're in the market for a full time 4WD car you might want to avoid such models and go for the real thing."

Well he is both wrong and right but don't worry. The Haldex can be programmed to whatever differential you want. I would be a lot more concerned about the Volvos using the Haldex (not to mention their old system), since they use 95% front 5% back until the front wheels lose grip.

There are two main AWD systems within the VAG as far as I know.

1) quattro - Torsen (for engines mounted straight)

Audi quattro

The quattro® permanent all-wheel drive has a long tradition – more than 20 years. On the permanent all-wheel drive quattro® power is distributed as needed to all four wheels. This system provides high levels of active safety, and dependable traction on virtually all surfaces as well as excellent road holding, even in cross-winds. It is superior to manual all-wheel-drive systems because of this “permanent safety advantage”. On cars with longitudinally installed engines, a Torsen® differential distributes power and compensates for differences in wheel rotation when cornering; if the car has a transverse engine, these tasks are performed by a Haldex® clutch .

2) Haldex (actually made in Sweden )
for engines mounted 90 degrees.

Haldex

Audi uses a Haldex® clutch to transmit power on its cars with transverse engines and quattro® permanent all-wheel drive. It has been specially adapted to this configuration and distributes the drive force variably between the front and rear wheels, preventing the build-up of stresses in the power train when cornering (like the Torsen® differential). The Haldex® clutch has advantages for all-wheel drive in conjunction with a transverse-mounted engines. A lot of different information is needed to distribute power to the wheels – for example, the engine speed, torque, wheel speed and anti-lock braking system (ABS) function.
*) Trademark of Haldex AB, Landskrona, Sweden

There is more to find in the glossary if you want to read more.

[Rhaps]

The article says that the Audi A3, S3 and TT is "false" 4WD, this is true, These cars does not use a torsen differencial, hence not a quattro, they use haldex. Despite these cars wears the quattro name, this is probably due to the strong marketing position the quattro trademark have, and to tell Audi customers that this is a 4x4.

More info on www.howstuffworks.com

[Erik]

Why should Haldex be a "false" AWD?

In my opinion it is far better than the mechanical Torsen if the setup is ok.

[Rhaps]

Well .. it might be my english, what I ment with "false 4WD" is that it is not a permanent 4WD.

[sukebe]

Thanks for the information. It really helped!!

[remedy]

What's not permanent about it? It's not 50-50, but it always transfers some power to the rear wheels, it just transfers more when the front wheels start to lose grip.

[Rhaps]

Ok, I have checked my sources about the haldex, and I was wrong. :blush: The Haldex will always transfer some power to the rear wheels, I tought it didn't, my bad.

[Kram]

Haldex is called false 4 wheel drive because it is a reactive system. It only transfers torque if there is different speed between the two shafts of the two axes (front and rear in this case). The Torsen differential, that is far more expensive, react to torque difference and act before any slippage could occur.

[rennen]

EDIT: oops my bad , sorry...