Haldex 5 - XDS+

2.5 I5 20v TFSI - 335 bhp
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Dave_Hedgehog
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Haldex 5 - XDS+

Post by Dave_Hedgehog » Thu Dec 05, 2013 5:30 pm

Mostly a place holder so I can find this, but I assume this is on the new S3 and possibly on the new RS3 (if there is one)

http://www.youtube.com/watch?v=9apQu8lpPE4
The Hedgehog, creator of RS4.org, back in of the RS fold yet again, third time lucky :)

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dbm
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Re: Haldex 5 - XDS+

Post by dbm » Thu Dec 05, 2013 11:07 pm

Still no torque vectoring though. Saab had this on their Haldex-based cars back in 2011, and Nissan Juke has it for #^€$* sake!

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Re: Haldex 5 - XDS+

Post by adsgreen » Fri Dec 06, 2013 8:50 am

dbm wrote:Still no torque vectoring though. Saab had this on their Haldex-based cars back in 2011, and Nissan Juke has it for #^€$* sake!
Yeah it does? It brakes the inside wheel during cornering to apply more torque to the outside wheels?

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Re: Haldex 5 - XDS+

Post by dbm » Fri Dec 06, 2013 9:26 am

Torque vectoring directs power to the outside wheel, it doesn't need to brake the inside wheel.

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Re: Haldex 5 - XDS+

Post by adsgreen » Fri Dec 06, 2013 11:43 am

dbm wrote:Torque vectoring directs power to the outside wheel, it doesn't need to brake the inside wheel.
What do you think happens when you brake the inside wheel?
Torque will always go to the wheel via the route of least resistance. Think of what happens when you have an open diff with one wheel on mud - the slipping wheel gets 100% of the torque. So if you brake the inside wheel you also will get a proportionately more torque going to the outside.

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Re: Haldex 5 - XDS+

Post by dbm » Fri Dec 06, 2013 11:07 pm

Using that mechanism you can get at best 50-50 power distribution across the rear axle. With torque vectoring you can push more than 50% of the power to the wheel with traction - getting a rear-wheel drive effect.

This page describes the effect as implemented on the RS4:
http://www.audi.co.uk/new-cars/rs/rs4-a ... dling.html

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Re: Haldex 5 - XDS+

Post by Dave_Hedgehog » Sat Dec 07, 2013 6:31 am

dbm wrote:Using that mechanism you can get at best 50-50 power distribution across the rear axle. With torque vectoring you can push more than 50% of the power to the wheel with traction - getting a rear-wheel drive effect.

This page describes the effect as implemented on the RS4:
http://www.audi.co.uk/new-cars/rs/rs4-a ... dling.html
Haldex is a compromise to save weight and space but in the real world the difference is not as noticeable as you might think, infact compared to most variants of quattro it feels far more controlled, most current quattros will understeer quite badly under power on cornering and on some will even lose traction on the inside front wheel, I was able to get monumental torque steer in the wet on the new RS6 to the point the car had significantly got away from me something i have never had in a haldex car (but then it would also spin all 4 wheels in 3rd in the wet lol)

The only recent Audi I have driven that felt it had a more controlled and responsive quattro system was the B8 RS4 (the R8 happily spins its rear wheels on take off :biggrin2: )

so for most people 99% of the time you wont notice much of a difference (This is qualified in saying the RS3 must be left in sport ESP to enable the front E Diff, and ideally not have the terrible conti tyres on the front)
The Hedgehog, creator of RS4.org, back in of the RS fold yet again, third time lucky :)

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Re: Haldex 5 - XDS+

Post by adsgreen » Sat Dec 07, 2013 11:19 am

dbm wrote:Using that mechanism you can get at best 50-50 power distribution across the rear axle. With torque vectoring you can push more than 50% of the power to the wheel with traction - getting a rear-wheel drive effect.

This page describes the effect as implemented on the RS4:
http://www.audi.co.uk/new-cars/rs/rs4-a ... dling.html
Same principle applies - try use the front brakes to get the effect of shifting power back.
I do prefer the r8 and gtr setup where the gearbox is flipped over at the rear. So in effect it's red with the option of 50:50 to the front (an even more if you start braking the rear wheels).
The issue though is highlighted with the gtr - it's has two props shafts... One from engine to rear mounted gearbox and then one from gearbox to front axle. Complicated and expensive.

The main driver though is that under 99% of driving conditions 4wd isn't really required so is just a drain on power and increases emissions. With the current legislation trends perm all wheel drive will start to fall out of the mainstream.

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Re: Haldex 5 - XDS+

Post by dbm » Sat Dec 07, 2013 6:06 pm

Just for clarity, I'm talking about the ability to push power left or right on the rear axle. Here is the full write up:
http://en.wikipedia.org/wiki/Saab_XWD

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Re: Haldex 5 - XDS+

Post by adsgreen » Sat Dec 07, 2013 10:03 pm

Yes I know what you are referring to.
That wiki page is not really what I would call a full write up.
For reference the new rs4 'torque vectoring' is still using one wheel braking in conjunction with a funky differential.

The eaiest, quickest and most controllable method of controlling torque sent to each wheel on a given axle is to selectively apply the brakes on the wheel you don't want the power to. It doesn't need a lot easier - you're not trying to stop the wheel. The slightest difference in effort between the two wheels on the same diff will cause a big difference. A good example is driving a big power open diff car.

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Re: Haldex 5 - XDS+

Post by Ricky.REP » Sat Dec 14, 2013 7:50 pm

Audi's torque vectoring involves braking the slipping wheel so the torque is then applied to the wheel with grip via the differential.....even the GTR's do it this way as it is very difficult to torque vector across an axle using the differential.

The R8 is different in that it uses a viscous coupling in the front diff to vector torque away from the rear axle....the prop shaft always spins at rear drive shaft speed.

This new Gen5 Haldex is mechanically the same as gen 4 except the control solenoid has now been replaced with a clever centrifugal bleed off valve.....

Majority of us won't notice....but always good to know the technology is pushing on!! ;-)

Regards Ricky

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Re: Haldex 5 - XDS+

Post by Dave_Hedgehog » Thu Jan 23, 2014 2:16 pm

The Hedgehog, creator of RS4.org, back in of the RS fold yet again, third time lucky :)

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