Awd, X, 4matic, 4motion....

[Alx]

Im not sure if this was discussed prior, but i was always curious who makes the better AWD system? I always felt Audi did, but i started believing it was BMW after driving a X 3'er.

This is all in regards too cars not SUV's.

What distinguishes a better system? Who has the better system, if there is one? Lambo, VW, BMW, MB, Audi, Subaru, Nissan, Porsche... etc....

There are so many versions and each i think does the same....

Anyone have any ideas on which performs and does the job best.

I do understand some systems are for road/track handling as others are for snow and rain. Sentiments guys?

 

[wltsm]

Audi are, I don't know if anyone has the video, but there was one posted on GCF ages ago, and it was of different cars driving up a ski slope, and the Audi didn't get stuck, while the BMWs and MBs, didn't get far at all!

 

[Alx]

would be nice to see, perhaps Yanni's might have that, but other than that what makes their systems better and is it overall a better handling system as well?

 

[Sayyaaf]

I have always wondered .. does Audi build their own 4WD system or it is another companies technology and they enhance it ... coz i dunno where i've read this .. the new Q7 uses BorgWarner 4WD system (maybe a thread by Yannis in GCA.com) .. what does that mean ? anybody ?

is BorgWarner another specialized company or it is just a technique in 4WD systems .. can some1 clarify this ?

 

[Zafiro]

I dont know which is best but my guess is Audi and Subaru. They've been making AWD for a long time. Nothing wrong with X-drive, probably works great too but I think Audi's system has a edge.


BTW. I posted that movie once but dont remember where I found it

 

[Snake Vargas]

BorgWarner make all sorts of automotive (and probably other stuff) things, like Bosch and Delphi and others. BorgWarner also make transmissions and turbos, as far as I know, and likely more stuff.

The best people for this thread would probably have been Martinbo and Yannis - the people with most knowledge about Subaru and also VAG/Audi. Oh well.

Anyhow, not all 4WD systems are created equal. There's many different sorts of differentials and where they put them, as well as whether they're permanent 4WD systems or torque on demand (ie. wait for slippage to occur before reacting).

Some Audi/VAG systems are Torsen (they're an OEM 4WD system supplier, I believe). I'm not quite sure off the top of my head what's so good, but er, last I remember it's a good sort. Permanent 4WD with torque able to be sent forwards or backwards.

However, some are Haldex systems, I think.. which are usually primarily front drive, but upon slippage, can send torque to the rear wheels. I think they tend to be slower acting, reasonable for everyday driving, but not the best for performance applications, IIRC.

Otherwise.. there's other systems such as in SUVs (I know you said car based Alex) where there's only one open diff in the middle (ie. active at all times) and individual wheels use ABS type sensors to monitor slippage and brake at will, reducing that wheel's spin and torque to zero, hence 'sending' it elsewhere somewhat.. I think BMW's X-drive is one system, as well as MB's passenger car 4Matic (E-class) system. Ok for everyday driving in slippery conditions such as ice, but not ideal for performance applications.

Well, I'm sure I've made more than a few mistakes. I know a mishmash of things, but don't know where it all fits together.

 

[wltsm]

Am I right in saying the Haldex system, is used on the golfs with 4 motion?

 

[Snake Vargas]

Yeah, somehow coincidentally I am reading a review of the Golf GTI that mentions that the R32 uses a Haldex system. I suppose the 4Motion Golfs use the same.

 

[Zafiro]

Porsche are going to use it and Volvo already use Haldex as well

More cars:
http://www.haldex-traction.com/default.htm

 

[Alx]

So is VAG and Haldex the most popualr or best of the AWD systems? Lambo bieng Audi, i wonder if they use VAG?

 

[Snake Vargas]

Not sure what Lambo use, but VAG (btw, that's Volkswagen Auto Group) also use some Torsen systems, probably most notably in the RS4. I'm not sure whether or which ones, but some 4Motion badged vehicles may also be Torsen - ie. 4Motion doesn't necessarily mean Haldex.

 

[Zafiro]

Not sure what Lambo use, but VAG (btw, that's Volkswagen Auto Group) also use some Torsen systems, probably most notably in the RS4. I'm not sure whether or which ones, but some 4Motion badged vehicles may also be Torsen - ie. 4Motion doesn't necessarily mean Haldex.

Here is the link again.

http://www.haldex-traction.com/awdclub/carmodels.htm

 

[Alx]

OOOOOOOOooooooooooh...... Bugatti Veyron is on the list.

Didn't think they made their AWD system too.

Lots of performanc cars on the list....

Great find Just_Me.

 

[Sayyaaf]

SV: thanx man .. so actually Audi's quattro is not supplied by a single vendor ... but it depends on the model ...

this is interesting ..

 

[Alx]

That list is pretty impressive, from super cars to minivans.

Must be one of the better AWD systems i suposse.

 

[martinbo]

That Haldex coupling is a brilliant unit no doubt - it has to be because it has its work cut out for it! The reason I say this is because the typical Haldex system drives only two wheels in normal driving conditions. However, as soon as the system detects wheel-spin it needs to direct a great portion of the total engine output to the rear or opposite axle. So guys, though the Haldex coupling is state-of-the-art, this does not mean that this is the most complete AWD package.

I could go on forever about grip and four-wheel drive and all but I'd just end up boring you to tears. So, here's martinbo's concise and abridged appreciation for what is all-wheel drive in road cars:*1

There are 3 main types of AWD on any given vehicle and their fundamental behavior is governed by the single most important component of any AWD system: the centre differential.

1. Semi-permanent, reactive AWD
You'll notice the list of cars in that Haldex page, most of them are FWD cars and the Haldex LSC acts as a limited slip centre differential that reacts to front wheel slippage (very quickly mind you) to send torque aft to the rear axle. Once the slipping stops, so does the all-wheel drive. So, the ultimate benefits of AWD *2 aren't attained and the car behaves predominantly in much the same way as its FWD counterpart might do i.e. the vehicle has a natural tendency to understeer quite dramatically when pushed close to the limits of adhesion. Examples are the Audi S3, Golf R32 and Volvo XC70 Cross Country.

2. Permanent, reactive AWD
This is a much better system - especially if the torque split is 50:50 or close to that - as the benefits of AWD are already in place and working for the driver. Because the torque split is so even, the wheel that has the most grip is doing most of the work and so, even in the event of wheel spin the limited slip device such as a viscous coupling has much less work to do in terms of apportioning a percentage of torque to the axle with most grip. It's quite simple: take a powerful car like an R32 with 320 Nm and divide that between the two front wheels = 160 Nm per tyre. Take a US spec STI with 400 Nm divide by all four wheels = 100 Nm per tyre. So the limited slip diff has a more even spread of torque and thus has less to do when moving it from front to rear. The LSD reacts to losses in grip at a given axle. Subaru is a prime example of this system as is Porsche and to a lesser extent, BMW's x-Drive which uses electronic sensors to signal the transfer of torque. Such a vehicle has a natural tendency to understeer when pushed beyond the limits of adhesion.

3. Permanent, proactive AWD
The ultimate AWD systems, the most notable example being Torsen as found in the Audi S4, RS4 and RS6 for example. It takes the above concept of AWD to a different level. The Torsen centre differential is a worm / planetary gear arrangement that is a mechanical work of art. It's name is derived from TORque & SENsing because really that's what it does: senses which axle has the most torque based on the frictional co-efficient or the amount of grip that that axle has. It reacts early on to subtle changes in torque before grip is lost. Hence, my term proactive. This is the ultimate in LSD technology in my opinion.

So there you have it. Please ask more questions but remember that eventually you will reach my level of technical incompetence.

*1 I say road cars simply to eliminate other types of 4x4 systems on off-road utility vehicles like pick-ups and heavy duty off-roaders for the purposes of this discussion

*2 The primary benefit afforded by true all-wheel drive is to halve the amount of power being sent to any one axle. Quite simply, in a good AWD system the power is divided permanently between the front and rear axle up to a perfect 50:50 front to rear ratio. This effectively halves the force of the engine output acting on a wheel reducing the potential for loss of grip.

 

[Sayyaaf]

martinbo: thanx .. well said and explained ..

 

[wltsm]

Martin, I've just noticed you are a mod, I'm sure you'll make a great mod, with your unbaised views and great technical knowledge!

 

[Zafiro]

Martin, I've just noticed you are a mod, I'm sure you'll make a great mod, with your unbaised views and great technical knowledge!

Probably the reason why HoH is leaving

 

[Sayyaaf]

Probably the reason why HoH is leaving

Yes i thought the same ..