AWD Drive Systems
 

Can anybody explain the different systems out there?

Subaru is pretty proud of their 50-50 split all the time -- or whatever they do. They say it is better than the others.

Then there is the VW 4XMotion permanent four-wheel-drive on the Tuaregg...

MB has something they think is special...

None of these are locking diffs (tho Honda Pilots can 'electronically' lock the diff. apparently).

I am thinking in terms of snow; mud & gravel roads, not rock crawling or anything like that...

I can't explain how they all work but I have owned 2 AWD vehicles.

A '98 Subaru Legacy GT and my current ride the '02 Mountaineer AWD V8.

The Subie was awesome in foul weather.
The Mountaineer is awesome in foul weather.

I have also owned a 98 Explorer with the Control Trac system that sensed tire spin and electronically controlled the 4WD system - it sucked. You could feel every move it made.

Give me full time AWD - its worth the 1 mpg penalty or so.

You basically have two types (excluding trucks.) One that is four wheel drive all of the time, using a center differential to split the power and the other is two wheel drive normally, with a clutch that locks up to send drive to the rear, if the front tires slip. You want the first version, as the second one isn't transparent when it works. You can get seriously out of shape before it engages the rear wheels.

Manual locking differentials (as in the first Audi quattros) have essentially gone away in favor of Torsen diffs and things like that.

JR

My 90 964 has a 38 front / 62 rear split (I think) and uses wheel speed sensors, and a yaw sensor to direct power to whatever rear wheel or front axle as needed.

My mercedes has a different system. It has a know that you turn for 4X4 and if you turn it one more click, both differentials are locked up as well as the transfer case...

http://forums.pelicanparts.com/uploa...1253502028.jpg

Hmm...there is lot more.

Older Audi: locked or open middle differential
Later Audi: Torsen middle diferential
Older Porsche (964): planetary gear middle, lockable with clutch
Newer Porsche: RWD with visco clutch to front axle
Older Volvo: FWD with visco clutch to the back
Newer Volvo, Audi, VW: FWD with Haldex clutch to rear axle:
Older Land Rover: either RWD or AWD with locked middle
Older Audi V8: AWD with visco middle diff

etc...

I was under the impression that all Subies ran FWD until slippery condition appear.

From what I've read only the Jag X-Type outside of Porsche makes a rear drive bias split calling on AWD in poor conditions.

That's not completely true. Performance focused AWD cars like the Subaru STI, Mitsubishi EVO and the Nissan GT-R usually have adjustable torque split, in their most aggressive modes they are usually slightly rear biased.

VW and Audi use two different AWD drive systems. The Haldex system uses an electronic clutch to sense and limit slip. They also have a Torsen system that uses a mechanical diff, I believe it is 80-20 front-rear bias.

Hyundai uses a system on the Santa Fe where it is FWD most of the time and only sends power to the rear wheels when the fronts start to slip.

Lamborghini uses a system where it is RWD most of the time and only sends power to the front wheels when the rears start to slip.

I think any system that can suddenly engage certain wheels or violently shift power front/rear can make for unpredictable handling.

...which is why I don't like those systems. I've had 12 AWD cars (not counting the 4wd trucks) over the last 25 years and the only ones I'd buy are the one with a center differential that drives all 4 wheels all the time.

JR

volvo has one too. i was looking at this sporty turbo wagon that needs a motor, but the idiot wants $2500 for a car with 250k miles and a blown motor.
240 hp BTW, thought it night be fun. i have heard theirs is very expensive to fix if it goes bad.

So, even the newest technology part-time "sensing" AWD systems have lag effect? I was hoping they'd improved them by now...

And, who knows for sure what the Subaru Outback uses (not the various hot hatchbacks)?
- I thought they drove 4 wheels all the time (thru open diffs)...

I don't like them. I just sold an R32 that used the Haldex clutch. I could feel a lateral shift in the chassis every time it sent power to the rear, even on dry pavement. My wife used to have a Mercedes wagon, with the 2nd or 3rd generation 4-Matic system, that I could get completely sideways before it would send power to the front. And, I'm not talking about on snow either....

JR

This is what you want:

http://forums.pelicanparts.com/uploa...1253562669.jpg

will an old Quattro Audi will be better than a Subaru??

MY first choice would be a 1984-1987 Audi 4000 quattro, with the appropriate snow tires, sized correctly. I've had a couple of those and they have run rings around anything else I've owned, 4WD trucks included. With the right tires for the type of snow, it was not unusual to be able to use full throttle in first gear without wheelspin. I know the 4000 didn't have a huge amount of power....0-60 was 9 seconds... but still, it was pretty amazing. Tires are a huge part of the equation.

I have zero experience with Subarus, so I can't compare them directly.

JR

You guys have completely missed GM's Autotrack system used on their fullsize pickups. RWD unless the rear tires are going faster than the front - then the front gets power too.

The Envoy I rented had an even better system - in the mud, it was awesome - it seemed to work like the 964 system.

thx

I think that would be very hard to find around here, but will keep my eyes open for one.

I really need a 3rd old cult vehicle too...

Ok, here is a quote I found using Goggle:

Over the last several years Audi has started calling both their all wheel drive systems 'Quattro'. The first system is made by a company called Haldex and it is found in the Audi TT - this system is basically front wheel drive (90/10 front/rear split of torque) until slippage is detected and it then will direct more power to the rear as needed.

Audi's second system is the traditional Quattro system that you find in the A4, A6, A8, etc. It is technically complex with 3 different differentials - a center torque sensing differential to direct power front and rear as needed and front and rear electronic differentials to direct power left/right as needed. The real Quattro system is very good at providing traction where it is needed.

Subaru also has severl AWD systems. The first system, Active AWD found in most of their automatic transmission equipped cars (e.g. non-turbo Legacy/Outback) and it operates very similar to the Haldex system. The second system is called Continuous AWD. This system is found in most of Subaru's manual transmission cars. It uses a mechanical viscous center differential to split power 50/50 front and rear. Once slippage is detected, the system will react and send power to the wheels with traction. Subaru also uses the VTD (Variable Torque Distribution) system, which is closely related to Audi's Quattro system as it uses electronics to vary the power front/rear. I believe this system is found in higher end Legacy/Outback models. The STI uses a version of this system but has both front and rear limited slip differentials as well as the ability for the driver to select how much power to send front/back.

All the systems are very good with the Quattro probably being the 'best' albeit the most complex as well. The Continuous AWD system that Subaru uses is very simple and probably the most bomb-proof.

Audi's traditional quattro system is the one they invented back in 1980. The main difference is that the manually lockable center and rear differentials have been replaced with torque biasing systems like the Torsen. The other one is really the VW (4 Motion) system and is used on cars that have a transverse 4 or 6 cylinder engine. Audi's system is used on cars that have normal engine orientations, like the normal V6's (as opposed to the VW derived VR6) V8's, etc. The Audi TT and A3 are built on the Golf chassis, more or less.

Ironically, VW has built cars that had engines with a north/south orientation and these cars used Audi's quattro system.

JR

ok, so the the VW 4 Motion system is not very good?

watch this.
YouTube - Subaru Symmetrical AWD vs. Honda, Toyota, and Volkswagen

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the original quattro system was the best, haldex and viscus couples are what most use now