Author Topic: Interesting Haldex info  (Read 24995 times)

Offline topher

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Interesting Haldex info
« on: 15 August 2008, 08:57 »
Well interesting to geeks the likes of me anyway. A Haldex development engineer talks about the system and dispels some of the rumours. Nicked some bits from tech articles too.

I am employed by Haldex Traction in Landskrona. I work as a control software developer with a very interesting product, the Haldex Limited Slip Coupling. This is an intelligent coupling for distributing the torque between axles in an all wheel driven vehicle.It has some revolutionary new properties, the most evident being the intelligent way of dynamically controlling how much force goes to the front axle and how much goes to the rear axle. It communicates with other parts of the vehicle using the CAN bus.

The Haldex AWD system is used in the 1001 hp Bugatti Veyron!

The Haldex AWD system is also used in the Volvo S60 AWD, S60R, V70 AWD, XC70 and V70R, XC90, Volkswagen Golf 4motion and the Quattro version of Audi TT, Audi A3 and Audi S3, as well as on VW Bora, Skoda Octavia 4x4 and Seat Leon!!!

I develop some of the control algorithms affecting the car handling performance, and am responsible for tuning the coupling in one platform of a major car manufacturer.

My work requires me to travel a lot. In the winter test season, a lot of time is spent in northern Sweden, in the towns of Arjeplog, Jokkmokk or Arvidsjaur.

Since the late 1998, Volkswagen replaced the viscous-coupling Syncro system with a new system called "4motion". First shown in Audi TT and Golf 4motion, the new system uses a multi-plate clutch center differential developed by a Swedish company, Haldex, and computer software from the Austria 4WD specialist Steyr-Daimler-Puch. At this moment, it is only offered for the transverse-engined Golf IV platform, but there is no technical reason prevents it from applying to Audi's longitudinal-engined models.

The Haldex center differential is similar to Porsche 959's PSK system mentioned in the above, it is only smaller, simpler and cheaper thus making mass production feasible. The center differential is mounted near the rear axle and just in front of the rear differential. As shown in the picture below, its clutch consists of 6 discs ....


They are immersed in oil bath to reduce friction. Actuation is made by hydraulic pressure. Normally the input and output shafts rotate with a speed difference (could be implemented by different final drive ratio), therefore the discs are rotating relative to each other. When no pressure is applied, the clutch is not engaged thus torque will not be transferred to the rear axle. Increase the pressure on the multiplate clutch, the latter will be partially engaged, thus sending torque to the rear axle. The more the clutch engages, the more torque transfers to the rear axle.Computer determines how much torque to be sent to the rear wheels. Normally it is 50:50, but in tight corners when wheels on one of the axles is slipping, the driver can easily feel the torque is transffering from one to another axle. Volkswagen claimed 100% torque could be sent to either axle.

Compare with the Porsche 959's unit, Haldex's unit has 7 fewer discs in the clutch. This makes the Haldex unit more compact and cheaper. The down side is not capable to handle as much torque (959 had 369 lbft, Audi TT has 206 lbft). Besides, 959's discs were organised as 6 pairs of independent clutches, each actuated by individual hydraulic actuator. The Haldex has just one actuator acting on all six discs, again, this saves weight and cost. However, I suspect if it could vary the amount of torque split as precise as independent clutches.

Based on the journalists comment about the handling of Audi TT and Golf 4motion, it seems that the 4motion system performs even better than the traditional Torsen-differential Quattro. The age of Torsen Quattro is passing away.

Note: "4motion" is not equal to Haldex system. Volkswagen also use "4motion" to represent the Torsen-LSD system used by Passat. Therefore, "4motion" is actually a marketing nameplate instead of indicating the mechanical design.



Offline topher

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Re: Interesting Haldex info
« Reply #1 on: 15 August 2008, 09:00 »
They then go on to talk about some of the modifications available for the Haldex (info is a little dated now)

Having received numerous inquiries from spirited Volvo drivers about how to get their All Wheel Drive vehicles to handle more neutrally when pushed to the limit, EVOLVE (Volvo Tuner) and Haldex (manufacturer of the AWD units used on all AWD Volvos) have begun development of software enhancements to accomplish this.

Discussions first began at this year’s SEMA Show when the EVOLVE team and a Haldex representative first discussed possibilites of developing product together. Haldex explained to EVOLVE that as they began development with Volvo on the S60R and V70R, the Volvo engineers insisted on considerable understeer (the tendency for a car to push into a turn with the front tires losing traction) in the factory set up. Although the S60R/V70R are performance oriented vehicles, Volvo wanted to stay conservative in regard to handling as an understeer condition is much more easy to control for an inexperienced driver than an oversteer condition (the tendency for the rear of the car to swing around with the rear tires losing traction). This is quite understandable considering the Volvo safety philosophy. However, for capable drivers that seek the ultimate in handling, a more neutral handling car will yield better cornering, more driving excitement, and quicker lap times.

After SEMA, the EVOLVE team meet with Ulf Ahlen (President, Haldex Traction AB) and Gabriel Beldie (Haldex General Manager, Detroit Office) to further discuss product development. It was decided that the next logical step would be to have Haldex show EVOLVE what can be accomplished by altering the software controlling the power distribution between the front and rear wheels. A date was set and preparations were made.

Haldex sent one of their software engineers from Sweden to meet EVOLVE at a racetrack near the EVOLVE office. A professional driver who does considerable evaluation work for Volvo and other manufacturers was called upon to assist in the development. Also joining them was a representative from VCNA who is intimately involved with S60R development.

The process started by the Haldex representative tapping his laptop directly into the Haldex unit under the car on a stock S60 R. With the interface in place, he had complete control over how, where and when the power was split between the front and rear wheels.

Most of the testing was performed on a wet skid pad in a controlled varying radius on a low traction surface, allowing for the most accurate evaluation.

After several hours of hard driving and a cooked set of Pirelli’s, Haldex proved to EVOLVE that far more neutral handling can be accomplished with software modification. By applying more power to the rear wheels under certain variables during cornering, understeer can be greatly reduced on Volvo AWD cars. They were able to feel distinct differences in the car's neutrality, particularly during throttle-on and return-to-throttle (from trailing-throttle or trailing-brake oversteer) situations. Mild throttle-on understeer is a good thing in most situations. It is the excessive understeer at turn-in and under acceleration that hurts laps times.

EVOLVE also learned that the S60 R will never be a drift car with big, throttle induced oversteer slides. This is due simply to the fact that Volvos are primarily front drive cars with power being sent to the rear wheels as needed. Haldex was quick to point out that their set up on the new Lamborghini Gallardo is a different story as it is a rear drive car with power being sent to the front as needed. There are certain limitations that software can never overcome.

EVOLVE has determined that the combination of a Haldex software upgrade and their soon to launch sway bars will yield the perfect balance all driving enthusiasts seek.


And finally a word about Haldex upgrades specific to the R32

A haldex upgrade review
To answer a few questions..

1. Yes, I have one of these. Have had it since about a week before
the Playing in the Snow videos I posted.

2. Yes the stock R32 *can* do donuts like in the videos (done it), but
the Haldex HPP ECU makes it easier to initiate, among other things.

3. Yes it's plug and play. Requires a 4mm allen socket preferably on a
1/4" drive socket handle with short extension. (regular allen wrench
can't quite reach one of the two screws, and any bigger socket driver
won't fit in the limited space) Need to get the car up on ramps.. etc.
Will post full installation instructions probably in a new thread soon.
Takes maybe half hour, to 40 minutes.

4. It doesn't lose enough oil when changing out the valve to require a refill of the Haldex unit. It's just a little dribble trapped in the valve.

5. Peak torque transfer for the Haldex unit is usually rated at 2000Nm
(that's post transmission torque multiplication of the gears which
can be higher than that), but it's unknown whether Haldex with HPP
ups that limit or not. Their PreX graph shows it going higher, but that may
be for a beefier unit (the Haldex unit on the XC90 SUV mentioned above)
and not directly applicable to the HPP unit.

Offline topher

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Re: Interesting Haldex info
« Reply #2 on: 15 August 2008, 09:00 »
Does it work?
Yes.


Does it reduce fuel efficiency..
Don't know for sure, because I've been having too much fun with it, but
at highway cruising speeds fuel efficiency seems to be the same.


Haldex is pretty cagey about how and when it works but they basically said that the Gen I Haldex units in the R32 and TT use the priming pump for priming only and they can't produce actual pressure on the clutch with it. Gen III Haldex (Haldex with PreX) can. They admitted only that it's calibrated differently but that in addition to watching the throttle position it now watches the rate of change of the throttle position sensor and if
it sees it rising rapidly it initiates engagement of the Haldex clutch more quickly and aggressively.


If you mash on the gas midcorner, it'll send torque to the rear. This effect is reduced at higher speeds like the stock unit, to maintain directional stability and fuel efficiency. Overall, the only thing the Haldex engineer would admit to is that the "calibration has changed".


Ok, now let me address a common misconception (for about the 50th time).


Can Haldex send more than 50% of the torque to the rear?
Yes.


Can Haldex make the rear tires turn faster than the front tires?
No.


Those two answers are not contradictory.
Torque is an *applied* force. It must push against something to be measured at all. Torque cannot exist without a load, or in our case
traction. If the rear end has a lot more traction than the front and Haldex is
fully locked, then it *will* send more torque to the rear than the front.


Example, front tires on ice, rear tires on pavement.


Example, front tires on wet crosswalk stripe, rear tires on wet pavement.


In both cases, there will be more torque send to the rear than the front.
It is true, that all the transmission's torque goes mechanically through the front diff first before going to the propshaft, Haldex unit, and rear end. This means the rear tires can never *rotate* faster than the fronts. It's why the R32 will never be an oversteering monster. If you manage to get all 4 tires spinning/sliding, then yes you can hang the rear end way out (as shown in my videos), but on dry pavement, assuming equal traction at all four corners, most of the torque usually is used by the front tires before it goes to the rear, thus the oft quoted 100/0, 80/20.. 50/50 static split... etc.


However, this doesn't mean it's always going to feel like a FWD car.
When cornering, normally the rear tires follow a shorter path and thus rotate slightly slower than the fronts, not to mention that with 65% of the weight of the car on the front tires, they usually have a slightly smaller effective diameter due to deformation of the rubber thus turn faster than the rears. What this means to your car's handling is that if you can initiate full lock of the Haldex unit while cornering, it will force the rear tires to
turn the same speed as the fronts, causing them to increase their
slip angle to match that of the fronts, and the rear end will hang out
just enough to pretty much follow the same line as the fronts, which
from the driver's seat feels like pretty neutral handling. (oversteer/understeer/neutral.. it's all just about relative slip angles).


So.. What's it mean out in the real world with the R32 with this mod?

Ice and snow.
Makes the rear end quite a bit more lively. Easier to hang it all out, but if you turn ESP on, it doesn't interfere at all. So you've got "fun" and "safe" modes, and if you aren't sure, stick with "safe".

Wet roads..
Huge difference. Come into a 90 degree right turn at an intersection in 2nd gear, ESP off, crank the steering wheel over, mash on the gas, and the rear end just perfectly rotates to follow the front and it just flat out goes. No understeer, no big oversteer, just point and shoot. Wet roads are by far where this unit shines the most.


Dry roads.
Not as huge a difference, but can definitely tell that
it's there working, especially if you push the car to its limits.
Generally it means that on the throttle really hard is
the most effective and rewarding way through a corner. It won't
quite hang the rear end out by itself, but it does decrease
the on throttle understeer noticeably. The overall impression is of a
very well balanced car that just claws like hell to get through a corner
pointed in the direction you want. One needs to either be full off the
throttle to get it to initiate lift throttle oversteer, or full on the throttle
to get it to hold its line and tuck the nose in a little. Neutral throttle
through a corner, it'll feel stock.

Is it worth it?
Is to me. Basically if you want to maximize the performance of Haldex
then this is it. This is *the* Haldex mod. It's active enough on
all surfaces, for the kind of driving that I do (remember I turned my F1's
into slicks in 10k miles) to be well worth it. I'm looking forward to
seeing what it'll do on a track on sticky summer tires.

Komenda

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Re: Interesting Haldex info
« Reply #3 on: 15 August 2008, 09:10 »
So in summary the thingymabob spins round the oojimaflip that turns the fangle donger
« Last Edit: 15 August 2008, 09:24 by Komenda »

Offline Teutonic_Tamer

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Re: Interesting Haldex info
« Reply #4 on: 15 August 2008, 16:03 »
Can Haldex send more than 50% of the torque to the rear?
Yes.


Lies, and damned LIES.  A Haldex can NOT disengage drive to the front axle, therefore can NOT send more than 50% torque to the rear (Haldex driven) axle.

Ask any automotive engineer, and they will tell you that the application of possible variations of torque distribution is ONLY calculated when ALL driven wheels are on an identical surface - with grip.  That tw@t goes against ANY logical established auto engineering principles.  Don't really know why they have to come out with such crap, because, within its design parameters, the Haldex DOES work very well!

Of course he's not going to say it's shyte - he works for the fcuking company.  There is only one "Gerald Ratner" in this world.  :rolleyes:
Sean - Independent Automotive Engineering Technician (ret'd)
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Offline topher

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Re: Interesting Haldex info
« Reply #5 on: 15 August 2008, 16:32 »
What? His hypothetical and seemingly imaginary situation of zero friction under the front wheels and full grip at the back isn't scientific enough for you? :grin: He is talking about applied torque to the road though, not delivered through the haldex (and apparently contradicting himself) .. which as we both know would be a physical impossibility.. unless one of his modifications is a tiny motor attached to drive the centre diff.

Offline Teutonic_Tamer

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Re: Interesting Haldex info
« Reply #6 on: 15 August 2008, 16:44 »
Well interesting to geeks the likes of me anyway. A Haldex development engineer talks about the system and dispels some of the rumours. Nicked some bits from tech articles too.

Tophers' Haldex share options must be up for renewal!  :grin:

Quote
I am employed by Haldex Traction in Landskrona.

So you have a vested interest in "bigging it up" for your own company!  :rolleyes:


Quote
It has some revolutionary new properties, the most evident being the intelligent way of dynamically controlling how much force goes to the front axle and how much goes to the rear axle.

Bollox - the Haldex does NOT control how much "force" goes to the front axle.  That has long been decided by the engineers at VW (if we are talking about Dubs), and is determined soley by the transmission and final drive ratios.  Haldex can NOT change those!

Quote
The Haldex AWD system is used in the 1001 hp Bugatti Veyron!

Ohhh yes - so it is.  But what you fail to state is that the Veyron needs TWO Haldex units, because one Haldex can NOT do the job which just one Torsen can do!  :rolleyes:

Quote
My work requires me to travel a lot. In the winter test season, a lot of time is spent in northern Sweden, in the towns of Arjeplog, Jokkmokk or Arvidsjaur.

Thats nice for you.  Would you like a medal?  Do you have the chest of a man to pin it on to?  :rolleyes:

Quote
Since the late 1998, Volkswagen replaced the viscous-coupling Syncro system with a new system called "4motion". First shown in Audi TT and Golf 4motion, the new system uses a multi-plate clutch center differential developed by a Swedish company, Haldex, and computer software from the Austria 4WD specialist Steyr-Daimler-Puch. At this moment, it is only offered for the transverse-engined Golf IV platform, but there is no technical reason prevents it from applying to Audi's longitudinal-engined models.

OK, why then, if the Haldex is so good, has Audi not used it on their longitudinal cars.  Few would argue with the competencies of the 4wd system of the longitudinal Audi S and RS cars - and do so admirably without the need for Haldex.  :smug:

Quote
The Haldex center differential is similar to Porsche 959's PSK system mentioned in the above, it is only smaller, simpler and cheaper thus making mass production feasible. The center differential is mounted near the rear axle and just in front of the rear differential. As shown in the picture below, its clutch consists of 6 discs ....


LIAR, LIAR, LIAR, LIAR!!!!

The Haldex is NOT a "differential"!  It is merely a clutch-based coupling - in exactly the same way that an engine is connected to a gearbox.  When the clutch is "open", the crankshaft and the gearbox first motion shaft are entirely independent, and are free to rotate at different speeds, and even in different directions.  When the clutch is fully "closed", then the crankshaft and gearbox shaft rotate in unison, at IDENTCAL speeds.  A "differential" works completely different, using very differing engineering principles, which the Haldex does NOT, and can NOT use.  :angry:

Quote
They are immersed in oil bath to reduce friction. Actuation is made by hydraulic pressure. Normally the input and output shafts rotate with a speed difference (could be implemented by different final drive ratio), therefore the discs are rotating relative to each other. When no pressure is applied, the clutch is not engaged thus torque will not be transferred to the rear axle. Increase the pressure on the multiplate clutch, the latter will be partially engaged, thus sending torque to the rear axle. The more the clutch engages, the more torque transfers to the rear axle.Computer determines how much torque to be sent to the rear wheels. Normally it is 50:50, but in tight corners when wheels on one of the axles is slipping, the driver can easily feel the torque is transffering from one to another axle. Volkswagen claimed 100% torque could be sent to either axle.

Where????  VW have NEVER claimed a torque distrbution to either axle!  VW (correctly) only claimed that 100% torque can be sent to the front axle (in a front engined car).  More lies!  :sick:

Quote
Compare with the Porsche 959's unit, Haldex's unit has 7 fewer discs in the clutch. This makes the Haldex unit more compact and cheaper. The down side is not capable to handle as much torque (959 had 369 lbft, Audi TT has 206 lbft). Besides, 959's discs were organised as 6 pairs of independent clutches, each actuated by individual hydraulic actuator. The Haldex has just one actuator acting on all six discs, again, this saves weight and cost. However, I suspect if it could vary the amount of torque split as precise as independent clutches.

Which is EXACTLY one of the reasons why the Veyron needs TWO Haldex units!  :smug:

Quote
Based on the journalists comment about the handling of Audi TT and Golf 4motion, it seems that the 4motion system performs even better than the traditional Torsen-differential Quattro. The age of Torsen Quattro is passing away.

What - those "Swedish" journos who have a vested interest in Swedish companies?  Or was it muppets from the likes of MaxPower and the like, who you have fed and watered, and given a free "holiday" in some admittedly remarkable location.

Don't forget to tell everyone that "handling" and "traction" are two very different aspects of vehicle dynamics!  :smug:

And don't forget, it is NOT Haldex who determine the "handling" of a car - but I have a sneaky suspicion that the R&D and engineering and testing departments of VW and Audi will determine that!  Or are you saying that Haldex also determine spring rates, damper rates, roll centres, weight distribution, suspension types, suspension geometery, wheel/tyre offsets, tyre types - oh, and the most important item of all - the structural rigidity of the chassis/monocoque!  :rolleyes:

And where - exactly, is it stated that "The age of Torsen Quattro is passing away"?

Quote
Note: "4motion" is not equal to Haldex system. Volkswagen also use "4motion" to represent the Torsen-LSD system used by Passat. Therefore, "4motion" is actually a marketing nameplate instead of indicating the mechanical design.

Oh boy.  I think most VAG people know that already!
Sean - Independent Automotive Engineering Technician (ret'd)
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Offline Teutonic_Tamer

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Re: Interesting Haldex info
« Reply #7 on: 15 August 2008, 17:00 »
What? His hypothetical and seemingly imaginary situation of zero friction under the front wheels and full grip at the back isn't scientific enough for you? :grin: He is talking about applied torque to the road though, not delivered through the haldex (and apparently contradicting himself) .. which as we both know would be a physical impossibility.. unless one of his modifications is a tiny motor attached to drive the centre diff.

No he isn't.  He's specifically referring to scenarios where the front axle has completely lost ALL traction through ice.  Yet he fails to mention how the rear axle remarkably has full traction.  Oh - I know - the front axle is standing on the Bejing Olympic ice rink, and the rear axle is alongside the christmas tree at Santa Pod.  I'm sorry, but his scenarios are (a) as far fetched "fairy tales" as my ludicrous Bejing/Pod scenario, and (b) NOT the industry accepted norms.

The "Haldex way" has NEVER been the industry-wide accepted principals of describing torque distribution.  It is ONLY Haldex which have to resort to such sly and sneaky methods.

If you don't believe me, Google "Vehicle Dynamics Expo", blag yourself some free tickets to the next one - a nice trip to the US of A, and speak to any of the massed highly eminent and highly qualifed engineers from all walks, companies and corporations of the global motor industry.  None, appart from Haldex themselves, would support Haldex's method of describing torque transfer - not even the Yanks, which are well known for "pushing the limits" particularly in marketing.

Nope, this is just a sly marketing ploy by Haldex to purposefully mislead with information which does NOT conform to industry norms!  :sick:

And just to be utterly pedantic - Haldex is NOT a diff!  :tongue:
Sean - Independent Automotive Engineering Technician (ret'd)
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Offline topher

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Re: Interesting Haldex info
« Reply #8 on: 15 August 2008, 18:23 »
You missed my point.. he twisted the given example in such an ohso self-contradictory way from his original question relating to torque delivery, that his frictionless front wheels scenario manipulating the term applied torque (to the road) is comparable to jacking the front of the car in the air and letting the rear wheels run a rolling road. Useless, but that's basically his nice little imaginary analogy. (i think that part was actually written by an American.. pinches of salt available in the forum cafeteria)

Offline Teutonic_Tamer

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Re: Interesting Haldex info
« Reply #9 on: 16 August 2008, 10:03 »
Ahh, right, gotcha.  So what I accused him of was correct, though!

And I did realise that the Haldex employee was multi-quoting other authors, but I just couldn't be ar$ed to disect some of the drivel.  :rolleyes:  Should have guessed our American "friends" would be in there!  :rolleyes:
Sean - Independent Automotive Engineering Technician (ret'd)
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