Probably one for the more technical members amongst you but Im trying to understand where more 'advanced' 4wd systems have a genuine real world advantage over our Haldex 4 systems.

Last night I did a little off road 'detour' to get round a road closure - its the most Ive yet put the car through and I had my worries as to whether Id have the traction available but the car absolutely sailed through with just a little flashing of the off road light on the dash - traction wasnt an issue at anytime and again Ive been really impressed with what the car is capable of in this weather.

My interest comes after seeing an Audi Q7 trying to get up a slippery incline at the bottom of my road shortly after. It didnt even seem to really grip even at the bottom part of the incline and basically looked totally useless, spinning its power away at the wheels. :S

I have absolutely no doubt that the fact it was on huge low profile 'sports' tyres didnt help matters one bit but it did make me wonder what advantages this 'premium' full time 4wd system has over our Haldex 4 system? No doubt the guys gung ho driving style didnt help either :no: but if you were to set the playing field level and put winter tyres on a proper 'quattro' and the haldex 4 car - would the 'premium' system really offer a genuine advantage?

I'm not technically minded especially but as far as I understood it torsen differentials send power the the axle or wheel that is turning the slowest where as Haldex system sends power to the axle or wheel with the least resistance and electronic aids step in to minic a locking differential.

I'm sure someone more clued up will provide a better response.

The Audi Q7 is a permanent 4WD car using a Torsen type differential, whereas the Skoda Yeti uses a Haldex traction system that is reactive rather than the preventative Torsen type 4WD system.

That should mean Audi's permanent 4WD will make wheelspin less likely to start whereas the Skoda is having to try to regain traction after it's lost.

The Skoda will have better MPG and the reactive 4WD system is more than enough for 99% of people driving on slidey roads.

As for the Q7 on summer tyres - well, no 4WD system can be expected to perform miracles; the car needs some grip to start with and driving on summer tyres in wintery conditions is irresponsible in my opinion.

... would the 'premium' system really offer a genuine advantage?

This thread might be worth a read: LSD/EDL

Haldex is a genuine 4x4 system. More and more 4x4 vehicles are moving to haldex like systems.

The Q7 uses the BorgWarner system I believe.

The other major factor are the tyres being used. Winter tyres are still needed on a 4x4.

The major advantage for the 'avaerage' driver, is that haldex does the work for you. On a 'manual' 4x4 system, you have to know how to drive a 4x4 correctly in order to utilise it correctly.

I've driven a large number of different types of 4x4 system in the snow, mud and ice, haldex beats them all hands down (with the right tyres !).

Its' such a good system, someone without any snow/ice driving experrience can safely drive about in the winter.

The only thing missing from the Haldex system would be a centre-diff lock which it could do very easily since all it would need would be coding as it can do vary the torque split anyway all it would need would be to lock it 50/50 on demand. With torsen diffs having a centre diff lock makes them extremely good on poor traction surfaces snow/sand axle lockers are getting more and more uncommon now, I don't think the new Discovery even has a locking rear or front diff?

I think you have the "Premium" designation mixed up. The Haldex is in my opinion superior to the Torsen except in one respect: The Haldex requires an electronic input to work - many in fact, but the Torsen is purely self contained and purely mechanical.

The Torsen is a little hard to understand, but essentially, there is a bias built into the geometry of the gears, so the Torsen will only split the torque on the same axle in a fixed ration 60:40 as an example. This applies both to the center differentiasl and also to the axle differentials. On the other hand, the Haldex can put a majority of the torque on a single wheel.

Both the Torsen and the Haldex are really perceived to handle ON-ROAD slippery conditions including high speed wet roads in curves.

The REAL Off-Road systems, with locking center differential and limited slip axle differential are designed for off-road use and are superior under those circumstances. They are not good on hard surface roads, particularly not at highway speeds.

I think it a strong recommendation that Borg Warner just bought Haldex.

As you rightly say, large HiPerf slick tyres stink in winter. No amount of 4WD will help if the tyres cannot transmit the torque to the road.

Edited 21 December, 201015 yr by Agerbundsen

The only thing missing from the Haldex system would be a centre-diff lock which it could do very easily since all it would need would be coding as it can do vary the torque split anyway all it would need would be to lock it 50/50 on demand.

It can be done, likewise 'coding' Haldex to give a continuous 50/50 split is possible.

Performance for performance, you can't really beat permanent 4wd for traction but that does rely upon the correct selection of locking diffs, if they are available, and tyres of course. Haldex is a good system but my only limited experience of it was on an A3TDI 170 (PD) quattro and I found the combination of rubbish power delivery and the 'shunting' around of power pulling off the line annoying; the CR engine has got much better power delivery though.

As noted above, Haldex is always playing catch-up where as permanent 4wd is at the party already!

My interest comes after seeing an Audi Q7 trying to get up a slippery incline at the bottom of my road... It didnt even seem to really grip even at the bottom part of the incline and basically looked totally useless, spinning its power away at the wheels.

I still remember with suppressed fury the tagline when Audi first launched the Q7: "It's what quattro was invented for".

No it wasn't!

When it was introduced in the 1980s the Audi Quattro was almost revolutionary in that it put permanent four-wheel drive in a non-offroad-style vehicle. It wasn't the very first - for example, the Jensen FF preceded the quattro by about 15 years - but it was arguably the first from a volume manufacturer (Jensens were hand-built). Given the competition heritage of the Quattro, to suggest that quattro (which is a registered VAG trademark) really belongs in a bloated* soft roader is tantamount to heresy! To add insult to injury, the Q7 actually uses a Borg-Warner 4WD system rather than Audi's own "true" in-house quattro.

I was actually quite surprised that Audi agreed to the use of the slogan, since Audi owners tend to be quite knowledgeable about their cars and the company's heritage. Maybe it just shows that the Q7 isn't actually aimed at the "traditional" Audi market...

* eg it has such poor exterior vision that Audi had to invent a blind spot warning system for it!

I still remember with suppressed fury the tagline when Audi first launched the Q7: "It's what quattro was invented for".

No it wasn't!

When it was introduced in the 1980s the Audi Quattro was almost revolutionary in that it put permanent four-wheel drive in a non-offroad-style vehicle. It wasn't the very first - for example, the Jensen FF preceded the quattro by about 15 years - but it was arguably the first from a volume manufacturer (Jensens were hand-built). Given the competition heritage of the Quattro, to suggest that quattro (which is a registered VAG trademark) really belongs in a bloated* soft roader is tantamount to heresy! To add insult to injury, the Q7 actually uses a Borg-Warner 4WD system rather than Audi's own "true" in-house quattro.

I was actually quite surprised that Audi agreed to the use of the slogan, since Audi owners tend to be quite knowledgeable about their cars and the company's heritage. Maybe it just shows that the Q7 isn't actually aimed at the "traditional" Audi market...

* eg it has such poor exterior vision that Audi had to invent a blind spot warning system for it!

Amen to your whole post!

The only thing missing from the Haldex system would be a centre-diff lock

James, there is no center differential on the Yeti. The rear axle drive is a power take-off, so rotates with (presumably ) the same speed as the front axle. Locking the two axles 50/50 happens when the Haldex clutch goes to full lock. Hence the normal 10% drive on the rear is the fluid friction in the Haldex.

On very slippery stuff - like doing donuts in the snow, all four wheels spin, presumably with the traction control braling one of the front wheels.

The implied question mark about both axles turning at the same speed relates to the German Skoda site, which lists two different final drive ratios, but do not explain why. It could be that the PTO is not rotating at the same speed as the drive to the front axle, so the rear axle has a different drive ratio.

Just so there is no doubt, for real off-road work, three diff's with locks can't be beat with electronics. But that's not the Yeti's Baileywick either.

The Haldex system has always had a central diff, fitted before the haldex clutch. Its a standard open diff.

The haldex clutch controls which rear wheel recieves power, and how much.

Even with the traction control system turned off, the Haldex still uses various sensors to determine where the power should go.

For reference, the diff on the right is the standard open diff from a Haldex 1 system. (its only the computer that has really changed with later Haldex releases)

(the unit on the left is front diff, as found in the gearbox)

If you're really interested, these can be upgraded to LSD torsen types units from Peloquin:

These combined with an upgrade of the Haldex control unit (the 'Blue' Haldex) make the system pro-active, rather than re-active.

There is also an 'Orange' control unit, which locks the system into full-time 4x4.

(the unit on the left is Peloquin LSD replacement unit for the gearbox)

Later releases of the 'Blue' haldex, as found in the Haldex v3 and above, give the use the option of 3 operating modes: Normal (re-active), Blue (Pro-active), and Orange (locked into 4x4).

You get a little switch installed to switch between the different modes.

With all these Haldex upgrades, the computer still uses sensors to decide where the power is needed most.

When the Haldex system is working alongside the traction control, the vehicles can effectively shunt all power to a single wheel.

Edited 21 December, 201015 yr by snow_muncher

The haldex clutch controls which rear wheel recieves power, and how much.

I'm not sure about that, and although I could be entirely wrong, I thought the Haldex clutch only connected/disconnected the rear axle which housed it's own open axle diff.

The Haldex system has always had a central diff, fitted before the haldex clutch. Its a standard open diff.

Not that I'm doubting your expertise, but is that still true on the Yeti's system?  The Erwin workshop manuals only show 2 differentials - front and rear. There's a gear at the front driving the propshaft, which goes straight into the Haldex coupling, which then drives the rear diff. The diagrams for the Haldex unit don't seem to show any sort of internal diff.

Edited 21 December, 201015 yr by ginandtonic

Apologies to all. I've been getting some of my 4x4 systems mixed up

( too much 'apres ski' ... :beer: :cocktail: :beer: - surprised I have been going on about which ski-wax is best to use with haldex )

The diff shown in my pics is fitted transversly (side-to-side) inside the haldex unit.

The unit can control which wheels recieves power via an 'eLSD'.

The Peloquin unit shown in my pics operates by backing up the eLSD with a mechanical LSD. I suspect the Peloquin is only really of use with an upgraded (Blue/Orange) haldex controller

Cut-away pic of a Gen2 haldex unit. You can see the normal open diff inside:

(Have to admit, don't see how the power is transitted side to side - there does only seem to be one one gear to drive the transverse diff)

The eLSD

ps

The Yeti has a bogo - standard Haldex Gen2 unit fitted. The Yeti is after-all a Golf mk.5 based vehicle

Edited 21 December, 201015 yr by snow_muncher

Apologies to all. I've been getting some of my 4x4 systems mixed up

( too much 'apres ski' ... :beer: :cocktail: :beer: - surprised I have been going on about which ski-wax is best to use with haldex )

The diff shown in my pics is fitted transversly (side-to-side) inside the haldex unit.

The unit can control which wheels recieves power via an 'eLSD'.

The Peloquin unit shown in my pics operates by backing up the eLSD with a mechanical LSD. I suspect the Peloquin is only really of use with

Cut-away pic of a Gen2 haldex unit. You can see the normal open diff inside:

(Have to admit, don't see how the power is transitted side to side - there does only seem to be one one gear to drive the

ps

The Yeti has a bogo - standard Haldex Gen2 unit fitted. The Yeti is after-all a Golf mk.5 based vehicle

The yeti uses haldex 4 as does the later generation octavia scout. :S

The Yeti has a bogo - standard Haldex Gen2 unit fitted. The Yeti is after-all a Golf mk.5 based vehicle 

This page would beg to disagree...  http://new.skoda-auto.com/com/model/yeti/facts/Pages/facts.aspx

I think you have the "Premium" designation mixed up. The Haldex is in my opinion superior to the Torsen except in one respect: The Haldex requires an electronic input to work - many in fact, but the Torsen is purely self contained and purely mechanical.The Torsen is a little hard to understand, but essentially, there is a bias built into the geometry of the gears, so the Torsen will only split the torque on the same axle in a fixed ration 60:40 as an example. This applies both to the center differentiasl and also to the axle differentials. On the other hand, the Haldex can put a majority of the torque on a single wheel.Both the Torsen and the Haldex are really perceived to handle ON-ROAD slippery conditions including high speed wet roads in curves.The REAL Off-Road systems, with locking center differential and limited slip axle differential are designed for off-road use and are superior under those circumstances. They are not good on hard surface roads, particularly not at highway speeds.I think it a strong recommendation that Borg Warner just bought Haldex.As you rightly say, large HiPerf slick tyres stink in winter. No amount of 4WD will help if the tyres cannot transmit the torque to the road.

not sure i agree on the driving front, torsion gives a much more predictable result when driving on dry/wet/ice etc

The yeti uses haldex 4 as does the later generation octavia scout. :S

Not so sure about that ... thought Haldex 4 had been designed specifically for (and licensed to) Saab (GM) for the 9-3 Turbo-X

http://en.wikipedia.org/wiki/Haldex_Traction

This page would beg to disagree... http://new.skoda-aut...ages/facts.aspx

That link does prove or dis-prove anything.

Is the Yeti not basically a re-badged re-shaped VW Touran (which in turn is adapted from the Golf mk.5 platform) ...

Thought the Saab system was the XWD (cross wheel drive) :wonder: Anyway from the Haldex site, which sadly appears to be less informative than it used to be :(

"

Historical Background

Since 1998 Haldex Traction produces intelligent AWD systems. The first generation Haldex Limited Slip Coupling (LSC) came in a VW Golf 4MOTION that same year and a year later it was presented in a Volvo S60 AWD.

The first gen Haldex LSC was based upon a unique patented differential pump that created a hydraulic flow proportional to the difference velocity over the coupling. With help of a linear throttle valve, activated with help of a stepper motor, the "stiffness" could be varied and the torque transfer controlled. One can see the Haldex system as a rotational damper with variable characteristics.

Later, in the year 2002 Haldex Gen II was introduced. This second generation of Haldex LSC is still using the unique differential hydraulic pump, but the linear throttle valve has been exchanged for a solenoid controlled proportional throttle valve. On top of that a pressure sensor is introduced and used actively for closed loop pressure (torque) control, which created performance improvements especially withih the limits of tyre-road adhesion. However, the mechanical-intelligence is still there for disturbances beyond the bandwidth largely determined by the CAN communication, e.g, slip control and u-jump. Also, it offers great robustness to poor signal quality and CAN signal loss.

In case of a broken CAN bus the fall back is a certain predefined stiffness valve, which is a compromise between traction and manoeuvrability. LSC´s without this differential pump have to shut off and leave you in the bush, because there is not such compromising pre-emptive torque. Too high and the drive line shows fatigue problems, too low and the lamellae will burn.

Generation III, on the market since 2004, is a further development of Haldex´ second gen. By adding a check valve the already available feeder pump (a small pump to activate the system) could, although limited, create pre-emptive torque capacity over the coupling. This solution is called precharge, PreX. In later verions of this generation the pre-emptive torque capacity has been increased by means of a large feeder pump.

The Haldex Gen IV was introduced in 2007. The cost driven developments has favoured the pre-emptive techniques from the heavy PreX solutions in Generation III to a Haldex coupling without a differential pump. Also, the proportional throttle valve has been exchanged for a proportional pressure reducing valve. In order to create fast response of the coupling a hydraulic accumulator is kept filled by the feeder pump. The pressure reducing valve controls the pressure drop between the accumulator and the piston which creates axial force onto the clutch package.

Soon after the introduction of Haldex Generation IV, the introduction of Cross Wheel Drive, XWD, takes place in 2008 on a global platform. Although XWD existed in conjunction with former generations as prototypes, it will fist become on the market together with the fourth generation Haldex LSC. XWD is basically an electronically controlled limitied slip differential that shares power pack and electronic with the AWD system. Smart design also enables the XWD to be sold as an option within the same platform".

TP

Is the Yeti not basically a re-badged re-shaped VW Touran (which in turn is adapted from the Golf mk.5 platform) ...

That doesn't prove or disprove anything either.   :-)  Skoda can pick and choose from the VW parts bin - that's the whole idea of modular platforms.

And the Yeti does indeed have Gen IV Haldex. There's an electric pump and a pressure accumulator there. On the Gen II Haldex it only had a mechanically driven pump.

If anything the Yeti is more like the Tiguan than the Touran. Buit yes the Yeti and later Scouts use the Gen4 system, can normally tell looking where the filler plug is for the Haldex unit, its on the front for Gen2 and on the side for Gen4

not sure i agree on the driving front, torsion gives a much more predictable result when driving on dry/wet/ice etc

Which haldex equipped car are you making this comparison against?

And do we mean touran - isn't that the 2wd only mpv?? Touareg perhaps?

Very interesting thread and there's no doubt in my mind that the yeti uses haldex gen 4. It's not reactive like my old octavia 4x4 turbo, it's very preemptive infact. :yes:

Edit. Double post

Edited 21 December, 201015 yr by FocusZtec

Which haldex equipped car are you making this comparison against?

And do we mean touran - isn't that the 2wd only mpv?? Touareg perhaps?

Very interesting thread and there's no doubt in my mind that the yeti uses haldex gen 4. It's not reactive like my old octavia 4x4 turbo, it's very preemptive infact. :yes:

Tiguan not Touran as mentioned before.

Haldex 1 required 70% wheel slip before it engaged the coupling, Hadlex 2 dropped that to 30% so yes it works much faster.

Which haldex equipped car are you making this comparison against?

And do we mean touran - isn't that the 2wd only mpv?? Touareg perhaps?

Very interesting thread and there's no doubt in my mind that the yeti uses haldex gen 4. It's not reactive like my old octavia 4x4 turbo, it's very preemptive infact. :yes:

well i have a decent level of experience as i have driven many from Tiguan, golf passat 4motions and i have owned an A4 quattro 50/50 and currently have a an a5 40/60

in my experience torsen feels more planted and predictable at the limit. others may find different. also get less understeer now.

****im sorry if my bad spelling and iphone autospell upset the local school teacher!!!!****

Edited 22 December, 201015 yr by kenny