Quattro or Haldex - which is best (discuss)?

[s4dreamer]

Couldn't let Bison post two semi-intelligent questions without throwing one in myself.

So, I was wondering the other day why VW/Audi use Haldex rather than the well-established Quattro system.

I actually have cars with both, so can compare them directly, and the Quattro is definitely superior if you need a quick start. Haldex waits for the front wheels to lose grip, then transfers torque to the back, leaving a second or so of poor grip, whereas with Quattro, you have power to all 4 wheels, so can launch much faster.

I assume that Quattro isn't used across the VW/Audi range due to cost and/or weight (although if it were a weight thing, why don't they use it in the Passat).

Does Quattro incur other penalties, like greater fuel consumption than a Haldex car ?

In what grip situations is Haldex likely to be better (if any) ?

[Colvette]

I did a lot of reading into this when I had my RSi - I'm fairly sure that the two systems are identical, but the quattro system uses better components (and is hence more expensive) which is why you can feel a difference.

The 4-Motion system definately uses a haldex coupling, though...

[fatcat]

I'm confused

I have Quattro but also have a haldex ECU - I know because my dealer changed it last year.

Have I a hybrid version

help

[s4dreamer]

No Pete, you have a car using the "Quattro" branding.

Your 4wd system is Haldex, whereas on the A4, A6,... the Quattro 4wd system is used.

And there is definitely a difference between the operation of the two (not just parts) because my A4 has never been troubled for lack of traction at launch, whereas the Golf 4-mo did scrabble a bit to start off (compared on the same road junction in similar conditions).

[Bison1379134007]

well scrictly speaking they are both "quattro"

IIRC The diff is transverse engines use haldex clutches (electronic) and the longdidual engines use a torsen (mechanical) AWD system.

not had an audi for a while but im still in the game

i guess in theory you'd get a marginaly beter responce from the mechnical unit is its always got some power the rear wheels while the haldex (IIRC) needs 5 degrees (thats 1/72 of a wheel rotation to you) of slip at the front before it diverts any power.

[fatcat]

Now I'm really confused, y'mean I have a imitation quattro system, what about the S3 brigade ?

Mind you, the handling, grip & traction on mine has never been in question, never scrabbled on quick getaways.

However on the track, I do slide 'a little', but never 'scrabble' - heaven forbid.

so, who wants to buy an imitation Tdi quattro then

[Chris_B]

[ QUOTE ]

not had an audi for a while but im still in the game

[/ QUOTE ]

Not bad for a post-Stella hangover either.

Yes, quattro is now a brand name used to describe a variety of AWD systems from Audi. "Quattro" used to mean a Torsen-based system, the latest being Quattro IV, but when the Haldex system arrived in the A3, the name became just a branding thing.

IMHO, the Torsen based system is better with sufficient horsepower (it has higher losses than a Haldex) as the split is 50/50 normally, and if I remember rightly, Haldex can't send more power rearwards than forwards, unlike the Torsen where up to 75/25 split is possible, depending upon the pitch of the worm gear's teeth.

[Colin M]

The traditional Audi "quattro" is a mechanical differential and provides permanent 4WD. It doesn't fit in the transverse engined A3/S3 range so they use the electro/mechanical Haldex system. This provides predominantly front wheel drive (for fuel economy I guess) and only starts moving power around when the front can't get a grip.

And don't forget, all cars have 4 wheel braking, so your quattro system is only useful for delivering power, it does not improve the braking or stopping of your car before we get into that discussion!

[Mollox]

Sorry If I'm repeating anything, but Reading these posts carefully makes my head hurt.

Pete – the ‘little’ audis * the Golf 4Motion (and the new Volvo R’s for example) run Haldex AWD. This is where we get our ‘Quattro’ from. Quattro in the sense that we have – or to be pedantic here – CAN have all four of our wheels driven.

The ‘true’ Quattro, and the Quattro that Audi have been harping on about for the last 20 years is that based around the Torsen differential and is fitted to be ‘bigger’ Audis, S4 and upwards.

I’m sure that those with the experience of both could add far more worthy comment, and what I said has probably just been said but I wanted to say it cos im hungover.

Re the Trev mentioning that the Torsen setup is faster off the line as you don’t have to wait for it to hook up the back wheels – interesting – never tried it but I’m sure you’re right. From what I have read though, people still rate Haldex as being pretty trick (well, until your ECU dies and you have to pay for a new one!) and I’d argue that its more efficient than Torsen as its only used when needed, therefore being more fuel-efficient and saving you on tyres. Trev did you say you have to wait a second or so? I’m sure its quicker than that for Haldex to shift the power about. I’m sure I’ve read its impressively fast and to be honest, on the road, it does its thing quickly.

As I’ve just had my Haldex ECU replaced, I have experience of driving without Haldex in the S3 and I can tell you that its not a fun experience. No composure, no stability and no fecking traction. I was lighting up the fronts like a goodun all over the shop! (I also had knackered ESP). With it all fixed now the differnce is astounding. Haldex totally tames the S3 and gives it supernatural powers.

It’s a bit poo though that Audi do pass it off as “the latest generation of the legendary Quattro technology” or whatever when they clearly just buy it from some Swedish company!

[Bison1379134007]

yeah a second or so is all bad and wrong... that 1/72 wheel slip before diverting power is feck all... if you dump the clutch on the s3 you can barley ever feel it.

So on a torsen can it divert 100% power the rear? or does it have a max split but just with a greater read/front ration than the haldex? a real wheel drive chipped rs4.... now theres some fun!

and how can i fit a haldex to my TVR?

[Colin M]

The Torsen can't "divert" power, the gearing is fixed. The mechanicals of a differential (search How It Works) will allow the other wheel on a split axle to turn slower than another, but there is nothing clever going on in a torsen system, it's all Massey Ferguson tractor stuff.

[Bison1379134007]

hmmm... ok so is there a system that does it? there must be right? its just not a torsen or a heldex.

[s4dreamer]

[ QUOTE ]

i guess in theory you'd get a marginaly beter responce from the mechnical unit is its always got some power the rear wheels while the haldex (IIRC) needs 5 degrees (thats 1/72 of a wheel rotation to you) of slip at the front before it diverts any power.

[/ QUOTE ]

The thing is though that with the Quattro (Torsen), power is already with all 4 wheels. However, with the Haldex, most of the power is with the front wheels until wheel slip is detected. Try flooring it on a rough surface on slight incline - you'll find (unless my Golf was well fecked, which I doubt) that the fronts spin for perhaps 1/4 or 1/2 rotation, then you shoot off like a rat up a drainpipe.

Try the same in an A4 quattro, and there's no slip - the car just goes.

I suspected that using Haldex also gave better fuel economy because it drives mostly to the front wheels in normal conditions.

Another question though... why not get the Haldex to drive mostly through the rear wheels (ie switch it around), and only drive the fronts when the rear starts to lose grip ? Is is "safer" (for numby drivers like me) to mainly drive the fronts ?

[Bison1379134007]

maybe its that.... or maybe its the fact that making the car truley rear wheel drives involves a more powerful system. Maybe thats why it won't let 100% drive the rear wheels...

[Chris_B]

[ QUOTE ]

The Torsen can't "divert" power, the gearing is fixed. The mechanicals of a differential (search How It Works) will allow the other wheel on a split axle to turn slower than another, but there is nothing clever going on in a torsen system, it's all Massey Ferguson tractor stuff.

[/ QUOTE ]

No, Torsen does divert torque front/rear. Open differentials are used to allow one wheel on an axle to turn slower than another, but it only splits torque 50/50. The Torsen isn't just an open differential.

The torsen diff uses a set of worm gears to transfer torque from the input shaft to two output shafts. With equal traction on both outputs, the split is 50/50. When one output starts to slip, the worm gears are shunted into a different plane (or something like that) and the torque split is altered. By changing the pitch of the "thread" on the worm gears, the maximum amount of torque split can be altered. It's even possible to make a Torsen diff with a pre-loaded split, for example 60/40 split under equal traction conditions.

Torsen Traction's OEM usage web page shows common Torsen diff type applications for major manufacturers. The product page shows the types they make. IIRC, modern Audi's use Type B (T-2) diffs.

[S3Bangs]

Now,

I remember reading about the haldex unit and how it works somewhere a while ago and kept a copy of what I read.

Now what you are about to read comes from the mouth (or fingers, cos it was typed) of the vice president of marketing, Ulf Herlin for the Haldex units. I am not taking any credit for anything but posting it with the intent of it being informative.

Re: 100% Haldex torque transfer.

There are situations where near 100% torque transfer to the rear axle

occur. An example is if the front wheels are on ice and the rear wheels are

on tarmac. In that case the front wheels have (almost) no grip. In that

case, the Haldex coupling will transfer all torque to the rear axle and

prevent front wheel spin. On uniform surfaces however, the coupling can not

transfer all torque to the rear axle. See below.

Re: Does torque transfer occur only during wheel slip?

We need slip over the coupling in order to be able to transfer torque.

That slip (rotational speed difference between the front and rear axle) is

created by different tyre rolling radius (front to rear) and drive slip

between the tyre and road. The rolling raduis difference can be created by

differently worn tyres (or different dimensions, something that should be

avoided) and different load. In most cars, the front axle has a greater load

than the rear axle, which causes the roll radius of the front tire to be

smaller than the one for the rear tyres (given the same nominal size). This

gives us the possibility to transfer torque to the rear axle also when no

slip occurrs on the front tyres.

An interesting point.

<font color="red"> If you have differently worn tyres on the front and rear axles, the new

tyres should always be on the rear axle. This is true no matter if the car

is FWD, RWD or AWD, since you otherwise risk heavy and uncontrollable

oversteer in situations such as aqua planing. In this case, putting the worn

tyres at the front also helps not to reduce the maximum transferable torque

(maximum rear axle torque). </font>

During cruising which a constant velocity, we have the possibility to

transfer up to 40-45% of the torque to the rear axle, given nominal tyres.

During acceleration, the weight transfer increase the front tyre slip and

decreases the rear axle slip, giving us the possibility to achieve more or

less the same torque distribution as the dynamic weight distribution.

Generally speaking, depending on the vehicle somewhere around 60-70% is

possible to achieve during a full acceleration. Note that we are still

talking about a uniform surface, with no spin on the front wheels.

When cornering , there is in most cars a tendency for the inner front wheel

to lift and spin. In that situation, we can increase the torque transfer

even further.

So far I have only spoken about what possibilities there is to transfer

torque. How much is actually transferred depends also on how the Haldex

coupling is controlled. The engine torque and gas pedal position are

together with the wheel speeds and the engine speed the most important

signals that are used in the control. Brake, ABS and ESP signals are also

very important for enabling co-existance between the AWD system and the

ABS/ESP system. We control the coupling in order to prevent wheel spin as

well as removing it quicky if it should occur.

Re: Dependency of torque transfer with speed.

It may vary a bit with speed (and road surface), but without going into

details a figure of around 10-15% would be typical. It is enough to help

stabilising the car while at the same time saving fuel and reducing the

temperature of certain driveline components. As soon as the driver starts to

accelerate or decelerate, more torque is transferred.

Re: Torque Transfer:

In general, a higher percentage of the torque is transferred

to the rear axle in low velicities than in high ones. This is partly due to

the fact that the total available driveline torque is larger at lower speeds

(and lower gears), thus causing more weight transfer to the rear axle. In

order to achieve consequent handling characteristics (as well as optimised

traction), more torque must then be transferred to the rear axle.

The Haldex coupling is completely compatible with ABS and ESP systems.

In order to optimise the performance of the ABS/ESP system, it is possible

to open the Haldex couplng during ABS braking or a stability control brake

intervension. The ABS/ESP antispinn and stability control also depend very

much on being able to calculate the vehicle velocity. That is very easy with

2WD, but as soon as you have the possibility of four wheels spinning it gets

very complicated. The Haldex coupling and ABS/ESP system interface make it

easier to obtain a good reference velocity.

In the cars where the Haldex coupling is available today, additional signals

available with ESP are not used. We do however have software using these

signals. This enables further optimisation of handling performance and life

span of driveline components.

During calibration of the Haldex coupling , we try to optimise the traction

and handling performance of the car. These are however not the only aspects

that are important. The final calibration is alway a compromise between

traction, handling, the life span of driveline components, temperatures in

driveline components, fuel consumption and more. If the car manufacturer

wants the same calibration to be used in several different cars, a new

compromise has to be made. Different manufacturers do have different

strategies about this. Some tend to let many cars share the same calibration

while others want to optimise each car individually.

Thats it. I hope you found it informative enough as I did.

[Mollox]

Haldex is stupid

[ QUOTE ]

An example is if the front wheels are on ice and the rear wheels are

on tarmac. In that case the front wheels have (almost) no grip. In that

case, the Haldex coupling will transfer all torque to the rear axle and

prevent front wheel spin. On uniform surfaces however, the coupling can not

transfer all torque to the rear axle. See below.

[/ QUOTE ]

in this instance the Haldex ECU should summon REVERSE gear. Whats the good in shifting power to the REAR wheels so the car can then move forward and get its rear wheels stuck on the Ice as well?

DUH!!!

[Gren]

From what I've read the Haldex sounds superior to me (not biased at all).

IIRC its faster to react and can transfer more power to different wheels. The real drawback (as many people see it) is how Audi/VW have implemented it - FWD until required. That can easily be remedied by a little box from Forge (a measly £1k) which will make the starting point programmable.

Then again you do get the lower transmission losses and better fuel economy of a FWD car - which is what you have and what you need most of the time.

As someone mentioned I think the Haldex option was chosen 'cos Torsen doesn't work with transverse engines. So no choice for all of us with Golfs - in whichever guise