jeremy

Just read Autocars write up of the new 911 turbo- apparently not quite as
all-conquering as it was hyped to be. It fell quite hard compared to the 4wd lambo last issue. Evo mag felt it to be somewhat ragged at Bedford as well.

Fact is the Turbo's 4WD for all the hoopla is really a Haldex in reverse, same as used by Ford, Volvo, Audi (A series,TT), VW and it seems BMW X-series as well, under a different name.

Question? Can a part-time 4WD system ever be as good as a full/real-time system?? Might the theory go something like this: a full time system does not need to react to a loss of traction becuse it is less likely to loose traction in the first place- due to the fact that the full time systems wheels were always being driven?
Or it my conjecture not always true; possibly as the latest version of the TT proves that if you can get the reaction time down enough the chassis simply cannot slip enough on the road to be noticable in the milliseconds before the Haldex is able to react?

Too bad no one does proper on-road comparisons of these sorts any more.

davecweed

the new 4wd lambo's, the ones that have come out since vag group ownership, have beening using the haldex in reverse as well! lol

the haldex can be programed to have more power going to haldexed wheels, etc, cos its a computer controlling it, u could have a 50/50 if u want, dont have to wait for wheels to start spinning, if programed in that way

in the s60r, as u enter a corner it sends 70% of the power to the back wheels, to give better turn in, then as u leave the corner it sends more to the front(s60r is the only one using the haldex in this way, could be wrong!lol), thats in conjunction with the 4c chassis system

Dracoro

The Haldex 4WD is used on vag cars (& volvo now I see) is used on those with TRANSVERSE engines. e.g. golfs, TTs, A3 etc.

The proper 4WD is used on vag cars with LONGITUDINAL engines, e.g. Audi A4, A6, A8 and Passats with longitudinal engines, e.g the W8.

See http://en.wikipedia.org/wiki/Quattro

I don't think the Lambo has the Haldex per se, I believe it's more a proper 4wd that send more power to the rear rather than the 50:50 in the Audis. Porsche does a similar thing with the 4wd 911s.

logiclee

When did Ford use it?

Cheers
Lee

Shark Man

Does it matter?

Scoobs have full time 4wd but and abolutely awful chassis and weight balance. Yet they stil gained critical acclaim. Amongst other things.

A system such as a standard Subaru AWD is basic. A viscous coupling, with the dynamic traits and flaws that come along with it.

Unless its eDCCD...which verges on the lines of Haldex, as it also has active electronic control to vary power distribution between front and rear axles.

GC8

Shark Man; you are a bitter man. Why not just set fire to the b*stard-thing and be done with it, eh...?

Simon

Shark Man

I'm hactually cleaning it up this weekend to sell.
Well, apart from its raining today, so that kind of stuffed that idea

Steve Whitehorn

iTrader: (13)

Great question Jeremy.
Dunno the answer - hope someone does.
To my old fashioned way of thinking. Haldex is in effect a form of traction control - a computer is buggering about moving power about to different wheels.
A good old classic scoob with a 50-50 front rear spit is just that. The only ´computer ´ involved is your brain. To me this means you are less of a passenger and you are totally in control.

My recent experience of computers controling cars...

I have driven most of the new generation of Volvos and taken them to the limits of their grip with traction control turned on and off. With it off - understear kicks in (nice and predictable for the less experienced driver)
With Traction control on the car grips and grips and the point when you ask too much from the tyres is further away but when it does go its overstear time (so although you are less likely to lose grip when you do its a bit more of a handfull of the less experienced driver with the TC turned on)

Personaly I feel you know where you are with a stearing wheel - 4 wheels with good tyres and permanent 4WD or RWD and all the electronic stuff thrown out and left at the side of the road. Perhaps I am old fashioned and missing the point?

Steve

davecweed

it does have the haldex in reverse, ie - all the powers at the rear wheels, then sends power to the front wheels, when needed, get your facts straight dude!

davecweed

which volvo's have u driven?

AudiLover

that doesnt make sense at all, "all the power at the rear wheels...."

Christ

Does to me... And what he describes is the opposite of Haldex (or in reverse as he puts it). Lamborghini is normally RWD, until the abs sensors (or whatever) detect the rear wheels spinning faster than the fronts, and then some of the power is tranferred to the front wheels.. The Haldex normally has power to the front, and if needed transfers to the rear.

Chris

Dracoro

I stand corrected on the Lambo thing. However, from a quick google, it's 'normal state' is 70/30 Rear/Front split untill splippage occurs as opposed to the haldex 100% front until splippage occurs etc.

Anyone know how the Porsche one works?

davecweed

go away u audi lover! lol

davecweed

not sure about other haldex users, but in the volvo s60r , its 90% front and 10% rear all the time, then more to rear when needed

there's one thing for sure its better in the snow than the scooby!

NWMark

the new TT and R32 use a similar setup to this, 90% front and 10% rear until slip occurs then it shifts more to the rear.

Mark

CrisPDuk

The Porsche uses a haldex clutch to drive the front wheels when necessary, from memory it is a nominal 10:90 split in favour of the rears in normal conditions, this is for 996 and prior models, but I'm pretty certain the new C4 & Turbo will follow the same line. Porsche aren't exactly noted for change.

As far as 'proper' 4x4 transmissions go, Subarus use pretty much a carbon copy of the quattro system, ie: a FWD gearbox with an additional output shaft connected to the rear wheels via a viscous coupling.
Mitsubishis use very complicated variation of the Ford/Jensen FFD system, a RWD gearbox with viscous coupling connecting the front wheels.
This basic difference between the two is the reason why a Subaru/Audi has an initial tendency to understeer before the VC starts to work, and the initial tendency of an Evo/Cossie is to oversteer, it's all down to which wheels start spinning to firm up the VC.

Diablo

Guys,

Haldex is just a brand name.

All the system is is a computer controlled clutch between the axles which can run from fully open to fully locked and anywhere in between and is the physical link between the axles as well as the torque splitting device.

In its most basic form, the original "haldex" equipped vehicles run as 2 wheel drive until slip is detected at which point the clutch is progressively locked and drive transferred to the other axle. Call it part time four wheel drive.

Honda CRV's run it in purest form - they are (or used to be) 100% front wheel drive until the fronts started to spin.

"Full time" four wheel drive (as in the subarus) run a full time torque split via a geared differential between the axles. The amount of slip (and torque distribution) being controlled by mechanical or electronic limited slip devices from viscous lsd's through the whole range to the clever stuff like the DCCD kit.

Whether the engine location is transverse or longitudinal makes no difference. RAV4s for instance are (or again, used to be) full time four wheel drive with transfer box, centre differential and transverse engine location running a base 50:50 torque split.

The Porsche appears to an electronically controlled multi plate clutch, but being a "permanent" system.

Its not clear whether the "clutch" is the physical link between the axles or simply the means of controlling the torque split, but my guess is the latter, as it used to be a viscous set up.

I can't comment on the new VAG systems, but the old ones (golf, TT, S3) were not permanent 4wd systems and hence very different to the porsche/lambo setups which are permanent.

I suspect a true "haldex" system would be unable to run permanently in full time 4 wd in anything other than a fully locked 50:50 split (which would be undriveable on tarmac) otherwise the clutch plates would overheat and burn out.

NWMark

Indeed correct you can now buy aftermarket controllers for the TT/S3/R32 that allow the haldex system to run 50:50 split all the time, although im not sure why it would be undriveable on tarmac?

Mark

Diablo

Mark,

Original haldex systems could only ever divert a maximum of 50% torque to the (otherwise) undriven axle by running fully locked as the clutch was the only connection between the axles. Its a clutch, so any slip between axles equals less than 50:50 distribution.

If fully locked, there would be no slip between axles. Try and turn on tarmac in this state and you get axle wind up.

Does anyone have a schmatic of the VAG system?

Steve Whitehorn

iTrader: (13)

DCW
New Volvos
Every - S and V 40-50-60-70 inc Rs
Only drove S60R once and didnt have the opportunity to put on limits of grip.
Did this however with V70R

Steve

stilover

Well, going by the recent post on another thread showing a "Haldex" driven Golf R32 beating a Impreza S204 round a track, I'd say the `Haldex` system ain't too shabby.
I'm waiting for the new S3 to be released to the press, as I'm considering getting one next year, and as that will have the `Haldex` system, it will be interesting to see what they say about it.

Personally though, I'd rather have full time 4wd. Whether it really makes a difference to every day driving is doubtful, but part of driving fast is confidence, and permanent 4wd gives "me" more confidence.

Steve Whitehorn

iTrader: (13)

´Personally though, I'd rather have full time 4wd. Whether it really makes a difference to every day driving is doubtful, but part of driving fast is confidence, and permanent 4wd gives "me" more confidence.´

Agree with you Stilover

Shark Man

It's not that serious an issue - unless your going round an oval track

I've ran my landy in full lock on tarmac over distances without handling issues or shearing a half shaft or dif locking pin (which usually happens when off roading - go figure ), its down to how strong the components are. Transmission wind-up is only there when cornering and is ofen released safely through tyre scrub on the inside wheels (open front and rear diffs will allow this slippage).

Now if you had a locking rear diff and rear diff also engaged as well, turning (or lack of) might become very interesting .

Long term durability could be questioned with a clutch engagement system. But slipper clutches as used in these systems are designed to slip, much like the clutches found used in a CVT gearbox, which slip all the time whilst in Drive and stationary and yet maintain a useful service life (it's also why a mechanically controlled CVT bogs down when you try and pull away quickly, as the gearbox senses the throttle opening and often locks up the clutch to quickly). Like the cluth with Haldex, it only wears when it is slipping i.e not fully open, and not fully locked. So it can go forever in either state, as long as the tranmission components can withstand the extra tourque of wind-up during cornering.

An interesting point to note with Subaru's basic AWD system....Remove the rear prop shaft (or a front half shaft). Now try driving - you won't get anywhere very quick, it slips. As the slip rate of the vicous coupling is too high for the torque difference applied to it. Which suggest that maximum % power capeable of being delivered to each axle can't be much higher than 50% and the system is incapeable of giving a 100% or 100:0 split without incurring slippage, unless it has a DDCD (which btw, is a clutch based system - like haldex ) A clutch based system can achive a 100:0 split, and without slippage, but it can only do it only in one direction (interms of torque distrubution). And up to 50:50 BUT still with zero slippage the other way. If you did the same test by removing a half shaft or prop on a clutch system capeable of full lock up, the car would still be driveable.

TonyBurns

iTrader: (3)

Saw that vid, the S204 starting from the back, being stuck behind 2 cars and having a driver who liked to go around the outside all the time doesnt really show you what the car can do, but he got right up there from being stuck and he couldnt get passed the front 2 because there wasnt enough room (due to them being side by side most of the time) but if you want to see how the haldex system really performs then look at the times for the nurburgring, you may find its no where near the front of the pack when it comes to laps of that circuit (oh and the S204 did the quickest lap on that vid ) and note that audi need a 450bhp car to break the 8 min barrier on the ring, subaru need 276

Tony

stilover

I knew someone would bite

AudiLover

The scooby had 320-340bhp I cant remeber exactly right now, and audi has done it under 8 mins with 414hp.

Im sure the 265hp audi R3 will beat that though as it weighs 750kg! Actually disregard that, it wont have quattro.

jeremy

Ok,
Here are some in-depth links that discuss the issues very well:
http://forums.vwvortex.com/zerothread?id=266930

and even better but quite long:
http://forums.vwvortex.com/zerothread?id=2510539

and here:
http://www.tyresmoke.net/ubbthreads/...0/fpart/2/vc/1

Quote:
"The Haldex system is also programmable. The R32 and TT3.2
programming is more aggressive and activates earlier than
that used in the older S3, and TT225, and there's been
a recent improvement called Haldex with PreX that was
developed for the Volvo XC90 V8 that allows it to engage
pre-emptively by monitoring the rate at which the
throttle position increases, as well as lateral forces
and such. It's being sold as an aftermarket upgrade
in Europe already, and will be available for sale in the
US shortly. I've been testing the upgrade on my car
and it's good stuff. "

SO the Bottom line it would seem is that indeed up to this point, Haldex is/was a reactive system that needed some time/momentum in order to sort itself- proving in some circumstances to be less immediate and possibly less predicable than other Pro-Active systems.

However: It would now seem that the newer iterations of Haldex do work quite a bit faster so they may be "reactive" enough for most. Further, new/after-market computer mods can now turn the Haldex system into an actual full-time pro-active system- unfortunately I cannot seem to find much new/up-to-date info on these modifications? IT being two years since such modifications were made available it would seem that their effectivness or degree of development might be in question.

I'll end by saying that most drivers of Haldex cars that I have spoke to say that most of the time the system works quite well, however when driving hard on difficult (with bumps) roads the system can become slightly unpredicable. As for the latest, the new R32 seems not to have received the best of reviews by anyone, and the new TT seems still an unknown having not been put through any difficult road tests. JL

AudiLover

In sport auto I just read that the MK5 R32 has permanent 4wd

RB5_245

Actually other that off roading the haldex system has the advantage of giving a rwd car a bit extra to the front to stabilize things. Giving you the precision and handling balance or a rwd with that extra drive when the rears start to slip. In a performance car this must be the best way to do it.

A 50/50 split 4wd car is always inherently flawed. taking the classic impreza as an example, it's a well sorted chassis with good balance and gravity centre. The 50-50 split cars inherently understeer where the type r works very well in a road situation. If you remove the understeer with dynamics such as the way integrale you get a fidgety car that takes a bit more skill to drive.

I see it as a good modification to give 2wd cars the traction of a 4wd whist retain the balance of a rwd. It'll also help fix fwd cars flawes well. I think the need to lock the diff for a 50-50 split should prevent it actually behaving like a true 4wd though... that may actually be a good thing.

Maybe someone should send me to the nurburgring with a 911 turbo just to be sure