Haldex Quattro system

[kingbilly]

In regards to the Quattro system, the Audi website blurb states that -

"It ensures that engine power is permanently distributed between the front and
rear wheels as and when required."

I understand that when the front wheels loose traction, then power will be sent to the rear wheels to help it out.

However, just pottering along on a nice dry day, in a straight line...what is the percentage split of power between the front and rear wheels...? Would it be 100% front and 0% rear...? Or is there a minimum percentage sent to the rear wheels at all times...?

Thank you,
Billy

 

[kanecullen89]

I think it's either 95:5 or 90:10 on the haldex

 

[steve111b]

For the 8P I found 85:15 on the audi.ca web site. That is for a DSG car, so the number may be different for a manual. The 5th generation Haldex (on the 8V) may operate in some new way, but I have not heard any news about it. The Quattro Concept engages the Haldex while cornering.

To get a 100:0 you need to have a differential before the rear driveshaft. This does not happen on the 8P. The Chrysler 200 has this feature to save fuel. On the Chrysler the rear wheels are engaged when the windshield wipers are turned on, or the temperature gets close to freezing.

 

[ConS3]

In regards to the Quattro system, the Audi website blurb states that -

"It ensures that engine power is permanently distributed between the front and
rear wheels as and when required."

Depends which Quattro system they are referring to. The S3 is front biased using Haldex. The RS6 on the other hand is permanent AWD, so there is always a 40/60 split between the front and rear under normal driving conditions, but can send up to 70 to either end as needed.

I understand that when the front wheels loose traction, then power will be sent to the rear wheels to help it out.

However, just pottering along on a nice dry day, in a straight line...what is the percentage split of power between the front and rear wheels...? Would it be 100% front and 0% rear...? Or is there a minimum percentage sent to the rear wheels at all times...?

Thank you,
Billy

In "normal" driving conditions, between 10-15% is sent to the rears. Some times, 100% goes to the front. All depends on inputs.

 

[chrisboyle999]

However, just pottering along on a nice dry day, in a straight line...what is the percentage split of power between the front and rear wheels...? Would it be 100% front and 0% rear...? Or is there a minimum percentage sent to the rear wheels at all times...?

From BorgWarner;

"The Haldex coupling will constantly transfer some of the engine torque to the rear wheels. However, driving straight at about 100km/h with no major wheel slip does not require much torque transfer from a performance point of view. Instead the torque transfer can be optimized for low fuel consumption. In such a situation, about 10-15% of the total propulsion torque is transferred to the rear axle. However this is very dependent on the calibration of the particular vehicle model, which is customized for every customer."

 

[veeeight]

However, just pottering along on a nice dry day, in a straight line...what is the percentage split of power between the front and rear wheels...?

The front half shafts are permanently coupled to the (front half) of the rear propshaft, so whatever speed the front rotates at, the rear rotates at. In other words, there is a 50:50 drive (rotations) split between the front wheels, and the input to the Haldex.

In addition: Due to clutch pack drag and oil viscosity, there is about a 5-10% drag (not active engagement) within the Haldex unit itself, but due to the fact that it is just drag, this can be overcome relatively easy, so, with the clutch pack open (e.g.: Haldex Fuse pulled),and if the fronts lost traction, the rears (even though theoretically frictionally engaged by 5-10%) will not have enough torque available to be able to grip to drive the car. Only when the controller signals the clutch pack to engage/clamp (this is determined by various inputs, ECU, throttle position, rate of change of throttle, ESP switch etc.) - will you get the Haldex clutch pack engaged, and the rear wheels brought into play.

To answer the OP's question quoted above:
In a straight line, on a dry day, with no difference in rolling diameter of your tyres/wheels (therefore no slip), and no inputs requesting the AWD ECU to engage, therefore Haldex clutch pack open - it would be realistic to say that you have a near 100% front wheel drive car.

In engineering terms, ignore the 5-10% clutch drag (as this serves play no part in actually getting traction down on the rear wheels), in marketing terms, Haldex would have you believe that there is a permenant 95:5 or 90:10 split

 

[kingbilly]

thanks guys for your answers and explanations

 

[audicruiser]

The maximum drive to the rear wheels using Haldex is 50%.

As already stated, in normal driving it is a front wheel drive biased car.

 

[ConS3]

The maximum drive to the rear wheels using Haldex is 50%.

As already stated, in normal driving it is a front wheel drive biased car.

That's incorrect. Near 100% can be sent to the rear wheels in certain conditions.

Directly from a Haldex rep:

1. 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.

 

[Pulp84]

^ ConS3 is correct. Remember that the MQB VAG mid size platform has the latest generation of haldex (think generation 5) so its much quicker to engage while also being able to send 100% to rear wheels

 

[veeeight]

You are talking cross purposes (Mixing up "drive" and "torque").

The front:rear split is 50:50. This is determined by a mechanical gear take-off in the output of the gearbox.
Whatever rotational speed the front half turns at, the rear also turns at. In other words, the drive is 50:50, or identical.

The concept of "near" 100% torque available at the rear is theoretical! The only (theoretical) situation where "near" 100% torque can be available at the rear wheels is if the front end of the car is in the air, with no weight on the front wheels, and the rear wheels are on extremely grippy tarmac.

"Being able to send 100% to the rear" is slightly misleading marketing speak, as this implies that somehow, magically, the car can de-couple the front wheels and make the car a power over steering rear wheel drive monster. This can never happen, as the rear wheels can never turn faster than the front wheels.

You can have a 50:50 drive split (as the A3 8V is) and still have differing torque at the front/rear (eg: 20/80) as torque at the tyre is a function of the surface friction coefficient and weight of the car at each wheel/tyre.

so - audicruiser's statement of only 50% drive to the rear is technically correct.

It's all about how Haldex dress up their blurb to suit the best marketing

 

[ConS3]

It's not theoretical at all. Head to some countries that actually require a rear biased setup for day to day driving (like Canada in winter), and it indeed operates in a rear biased setup.

At the end of the day, change the Haldex controller and you can have whatever setup you wish.

 

[kanecullen89]

The way that the haldex is mechanically attached will only ever allow a maximum of 50% of power to be sent to the rear.

The haldex information relates to available torque. So if the front is in full slip mode then 100% of a available torque is at the rear because of the slip there is no torque at the front. It will still only be 50% power. It's hard to explain but the drive sent to the rear is sent directly from the front axle without a centre diff

 

[ConS3]

Ok. My misunderstanding here. Thought we were talking torque transfer.

 

[the_lecht_rocks]

with winter tyres, how good will the S3 perform in wet / snow conditions ?

 

[veeeight]

In the case of an aftermarket Haldex Controller (e.g.: HPA Competition Race Controller, the most aggressive controller):

If you look carefully, captured on a 4 wheel dyno, the turquoise coloured line (Rear Wheel Pwr) is never above the yellow line (Front Wheel Pwr) across the whole rev range (despite the controller 100% locking the clutch pack), you can never have more than 50% drive being delivered to the rear wheels. This is due to the mechanical nature of the power take off in the gearbox.

A Haldex car, no matter which generation, cannot ever be a power-oversteering, smoke-generating, fire breathing car, as the rear wheels cannot ever be driven faster than the front wheels.

 

[veeeight]

with winter tyres, how good will the S3 perform in wet / snow conditions ?

Compared to what though?

Will it be better than an S3 without winter tyres? Yes
Will it be better than a FWD A3? Yes
Will it be better than a RWD car? Yes
Will it be better than a 2014 Evoque with normal road tyres? No

It will be possible to get a S3 Haldex car with winter tyres stuck. All you need is one front tyre to spin, and one rear tyre to spin. The car will not go anywhere. (In this instance momentum, combined with switching ESP to Sport or Off will help get you out of this, but you will still be stuck in deeper snow/less grip).

People often confuse 3 things with Haldex (or 4x4). Traction, Grip, and Handling.

Haldex will improve Traction, but not necessarily grip, and won't necessarily improve Handling. If you're mid corner and understeering, Haldex will play no part in getting you round the bend even though the rear wheels ("sending 100% to the rear" haha) have traction. Keep the power down and you're more likely to end up in the hedge/ditch !

 

[dbm]

A Haldex car, no matter which generation, cannot ever be a power-oversteering, smoke-generating, fire breathing car, as the rear wheels cannot ever be driven faster than the front wheels.

Kind of. In poor conditions the car can deploy more power to the road via the rear. My TTS did this occasionally in heavy rain / snow and I got a rear wiggle.

The normal setting is to send as little power to the rear as possible, and only to send more when the front can't cope. You could programme the clutch to send more power than this (up to the ~50% max) and so get less of a FWD feeling. I believe this has been done with the Golf R.

 

[veeeight]

You can get less of a FWD feeling, but you will never get a RWD feeling. The best you can hope for is an AWD feeling.

Sure you can feel the rear "kick in", or wiggle, and then you are 4 wheel power drifting. But never power oversteer. (Well, maybe sometimes in the snow you can achieve this due to poor grip at the front and better grip at the rear. But not on equal mu surfaces)

The only oversteer you can achieve is lift-off, and both the Golf R and S3 8V are very happy to do this on demand, especially when the road is wet. I've even managed it in the dry with Conti's fitted

 

[snowfree52]

Compared to what though?

Will it be better than a 2014 Evoque with normal road tyres? No

Yes it will, even a FWD car with 4 winter tires will be better than a 4x4 with road tires, unless you're only talking about climbing a straight line and the snow is fresh. but try downhill with bends and you'll see.

 

[veeeight]

The 2014 Evoque has the new GKN Active Driveline system, in which you can not only inter-axle lock front and rear axles, but also cross-axle lock the rear wheels. This coupled with the ground clearance will give this car an advantage almost no other standard road going car has, in terms of moving through deep snow. This will far offset any advantage an S3 will have with winter tyres in terms of traction in fresh snow and gradients.

Granted, on wet roads and light snow covering, the S3 with winter tyres will keep you on the road better with the softer compound, but will give up the ghost sooner compared to the Evoque as conditions worsen. I know which one I'd rather be in during a heavy snowstorm.

 

[snowfree52]

and ? try asking rooney to play with flip-flops

what is the link beetween the road and the car ? the tires !

I go a lot to ski resorts, and it doesn't matter if the car is a 4x4 or not. no winter tires or snow chains, and you're not gonna go anywhere. How many 4x4 I went past ... because they thought they could get away with road tires and get stuck ...

I have a range rover also and yes, I can go in deeper snow but I have 4x4 tires on 16" wheels on it.

 

[veeeight]

Maybe you should compare apples with apples then.

There are situations where a FWD car with winter tyres is going to be better, and there are situations where a 4x4 with lockable diffs and road tyres will still outperform the FWD with winter tyres.

The biggest factors are the driver (skill), and yes, the rubber.

Rooney in flip flops will still play better than the majority of the population in a pair of expensive trainers.

 

[snowfree52]

when I go to ski resorts, I go with the A3, The range rover is actually there the whole year.

So when I overtake those 4x4, it's not with the range. Apples with apples

and remember, downhill, you have a 0WD car when you brake diffs and stuffs are not going to help you turn or brake

 

[veeeight]

Indeed. And you have a Haldex A3.

But you probably won't take it into deep virgin snow car park, whereas I would take a 4x4 in

 

[snowfree52]

definitely would use the range for that mission. but even 4x4 tires are no match for winter tires. At the end in this case it would be about ground clearance

but if you have a good 4x4 and good tires, even ground clearance is not a problem : https://www.youtube.com/watch?v=J9vtype3TzM look at 3min

 

[veeeight]

Good thing that was lovely dry pow, and not claggy wet snow!

He had BFG MT's on, with nice side tread blocks. I grew up with Firestone SAT's great for M&S, but horrific on road.

Good vid though

 

[snowfree52]

thanks ! I have it on my favs

 

[Flibble]

For UK winter, I'd take any car on winter tyres over any car on summers. While a 4x4 is good for deep powder due to ground clearance, for actually gripping compacted snow and ice nothing beats winter tyres.

 

[h5djr]

For UK winter, I'd take any car on winter tyres over any car on summers. While a 4x4 is good for deep powder due to ground clearance, for actually gripping compacted snow and ice nothing beats winter tyres.

Personally I thing the only thing that will beat a car on winter tyres is one with winter tyres AND quattro. Which is probably why Audi sell so many quattro models in countries like Germany, Austria and Switzerland where winter tyres are a legal requirement in winter.

 

[Fiddie]

I'm very interesting in Haldex Race for V Gen. I've seen some videos for the IV Gen but I don't see any oversteed or drift in any one. Maybe in V Gen can improve the controller?

 

[veeeight]

I wouldn't hang your hat on Gen 5 just yet. The main difference between Gen 4 and Gen 5 is the deletion of the accumulator, and a revised pump with integral "centrifugal"(!) pressure control valve.

Gen 4 was famed for its "Instant Traction" due to the pre-charge pump and accumulator being able to deliver hydraulic pressure to the clutch pack instantly in milliseconds, Gen 5 appears to be a simplification & cost-saving exercise, now building up hydraulic pressure in hundreds of milliseconds (no accumulator to store pre-charged fluid). How this translates in real life remains to be seen, but there is a forum full of unhappy Swedes moaning about Gen 5:

XC70 MY13 Haldex Gen 5 = Grymt slött mot Gen 4 . • Sveriges Volvoforum
(You'll need Chrome or similar to translate)

On YouTube there is a video of one guy in a XC60 Gen4 pulling another guy in a XC60 Gen5 in the mud, to demonstrate no discernible difference.

However, on the Audi A3/S3, it still relies on the car's 50:50 PTO, so you'll still never get the rear wheels over-driven, and so won't get the power oversteer you desire. 4 wheel power drift, yes, easy, even with the stock controller, just press and hold the ESP button to switch off (2-stage ESP) - and the clutch pack will go into permanent AWD lock.

 

[snowfree52]

or you could use food trays

 

[veeeight]

That, is only strictly to be done, in McDonalds car parks

 

[steve111b]

and the clutch pack will go into permanent AWD lock.

Unfortunately I do not understand this statement. Could you elaborate Veeeight?

My understanding is that the ESP off disables the ASR. With the ASR off, the throttle is no longer controlled by the ESP system. This allows the driver to mash the throttle without it being cut by the ESP system. The throttle is the key to engaging the Haldex. With ESP off the Haldex engages more often, because the throttle is never cut.

If I turn sharply on a snow covered road and hit the gas at the same time, the ESP system cuts the throttle. Next, I do the same thing with the ESP off and the throttle stays in action, with the Haldex engaging and the rear stepping out. With no limit on the throttle I can oversteer as much as I want until I am doing donuts.

With my 8P I only have the first stage ESP off. I guess that 50% of the ESC remains. Turn sharply on a snow covered road (ESP off), step on the gas and the back end steps out into oversteer. Now I keep my foot in it and the back end my swing like a pendulum and start to oversteer in the opposite direction. If this happens the ESC kicks in and does not allow this pendulum swing to continue.

When the roads are covered in snow or ice my 8P Quattro (ESP off) performs just like a RWD.

 

[veeeight]

ESP = ESC. They are an "umbrella" terminology, for a host of other technologies, eg: ABS, EDL, ASR/TCS, EBD etc.
ie: ASR one part of the technology that encompasses ESP.

You are correct in stating that when you press the ESP OFF button, it only de-activates some features of ESP, not all of them. In your car it will disable ASR/TCS, but not ABS, EDL or EBD.

It will also override the Haldex ECU input signals to say, "go into permanent AWD mode" - and the clutch pack will engage.

The electronic diff (front) (EDL) will remain active up to 50km/h in quattro cars, and 25km/h in FWD cars, even when ESP is disabled.

 

[veeeight]

Personally, I would be a little hesitant to say that a 8P/8V behaves like a RWD car in snow or ice, it's a unique surface where other factors aside from grip/traction (eg: momentum) play a bigger part than on say tarmac.


In the following video, we can see a Seat Leon invoke what looks like a (power) oversteer, he starts by unbalancing the car, handbrake, lifts off, the rear comes around, then powers out of the corner. Fortunately, it's a diesel (or he's got fuelling issues), so we can see when he floors it, and when there is no throttle. This is completely different to how you would invoke and drift a RWD.




Tiff also demonstrates just how different (and difficult) is is to drift a AWD car, and Jason is in a M3 - again, different techniques, Tiff has to flick the car to unstabilise it first, and lift off:





In a 8P/8V, on snow, you can play with power and stability and momentum to hang the rear out, sure, but you're not going to donut the car as tight as a true RWD car, as the front wheels are always going to be spinning and trying to grip. So on snow you can get a 4 wheel or AWD drift going much easier than on tarmac, but the same principles apply, de-stabilise the car, get the rear out, balance on throttle and steering. BUT this will be a different technique/tactic to RWD drifting.

If you have studded tyres, and load the boot up with weight (more torque transfer to the rear wheels), you can get a much better drifting experience on a frozen lake - again - the caveat is that snow/ice is a unique surface, and you would struggle to replicate this on tarmac - because the fronts will always be trying to drive you out of the drift, pull you straight, as Tiff demonstrated on the video above. Note that in the video below, he is almost always changing direction with momentum/lift-off, rather than the traditional RWD technique of breaking traction by throttle on.

 

[steve111b]

Thanks Veeeight.

I have attended several events which demonstrated these new technologies (ESP etc.). Applying an individual brake (ESP) and activating brake assistant were two technolgies that I enjoyed discovering.

When the EDL is working you can go to the back of the car and smell the rear brakes and feel the heat that the EDL generated.

 

[veeeight]

Yeah, I have mixed feelings about EDL.

For me, it's useful trying to get out of a snowy car park. I wouldn't really want to use it for other purposes (eg: to aid handling).

The S3 8V does just this, uses it to "torque-vector" by briefly applying the brake to the inside wheel to help the car around corners at the limit. Can't say I've ever felt it working, not like the Sports Diff on the RS4.

S3Alex on the 8P forum has the "proper" (mechanical) answer, he's fitted a Quaife Diff to his S3
Then again, he does have a ridiculous amount of bhp...........


edit: I have this feeling that EDL only works on the front, but could be mistaken.

 

[dbm]

edit: I have this feeling that EDL only works on the front, but could be mistaken.

This infomatic on the Golf 4Motion system suggests that it probably works on both axels: