50:50 Haldex for the RS3?

[clam]

Haldex is definitly has it's limitations:
- It is restricted between 100:0 and 50:50, and runs at 90:10 most of the time. (sort of a one-way differential)
- It's speed-sensing, as opposed to torque sensing. So it reacts to slip, instead of preventing it.

When I heard the 350hp rumour for the RS3, I lifted an eyebrow. The effeciency of Haldex is already questionable in its current applications. Transmitting 350hp and 335lb ft for 90% through the front wheels is simply insane.

Several rumours about a new Haldex system, and tailpipe's suggestion that Audi is working on something new, has led me to believe that the RS3 will offer a 50:50 Haldex system.

It should be simple really. You install an open centre diff up front, and the haldex clutch can now act a a slip limiter.
It would be a similar system as the acclaimed WRX. Only the the type of VC clutch would be different.

As we know, a differential distributes power based on resistance. The various ratios of the multi-clutch Haldex system can trick the open differential.
- If the ratio is the same (front-back axle speed), then the distribution will be 50/50
- If the ratio is smaller, the rear will have less resistance, and the diff will give the rear more power than the front.
- If the ratio is taller, the rear will have more resistance, and the front will recieve more power.

A rear biased traction would be possible, if the 'static' ratio is smaller than the front.
Its performance could match that of Torsen.

It would have one drawback though, same as the Subaru system. In zero grip conditions, the ratio doesn't make a difference b/c the resistance is zero anyway. So here there is no slip limitation.

Watcha think? Is this possible?

Personally, I can't imagine a 350hp RS3 using the current Haldex system.

[Audihead]

Originally posted by clam
Personally, I can't imagine a 350hp RS3 using the current Haldex system.

Why not? Volvo does it w/the S60 R. That car seems to work just fine. It has 300Hp & 295 Torque.

[clam]

The S60R is nice, especially price-wise, but it's hardly ass-kicking. If the rumours are true, the RS3 will have +50hp, +40lb ft on the Volvo. I think that will be stretching the FWD biased Haldex to its limits.

It probably won't happen, but it would be nice to see a full AWD system on the A-platform. Especially for the TT, whos competitors are mostly RWD.

[JavierNuvolari]

Mmmmm..... Why not use the new RS 4's layout??? after all it's an RS series right??

Cheers,

Javier

[clam]

It wouldn't fit. The RS4 has a longitudinal layout, while the A3 has a transverse layout.

The transverse layout doesn't leave room for a Torsen diff.

[JavierNuvolari]

hoooo.... i ok thx, I forgot about that :blush:

[Audihead]

Also don't forget about the DSG gearbox that is sure to make it in that car. It needs the transverse system as well, at least for now.

:s4addict:

[DanielT]

Originally posted by clam
Haldex is definitly has it's limitations:
- It is restricted between 100:0 and 50:50, and runs at 90:10 most of the time. (sort of a one-way differential)
- It's speed-sensing, as opposed to torque sensing. So it reacts to slip, instead of preventing it.

When I heard the 350hp rumour for the RS3, I lifted an eyebrow. The effeciency of Haldex is already questionable in its current applications. Transmitting 350hp and 335lb ft for 90% through the front wheels is simply insane.

...

Personally, I can't imagine a 350hp RS3 using the current Haldex system.

I think you need to study the Haldex design and application some more before you question it. Sure, it uses the axel speed difference (slip) to build oilpressure but it does prevent slip by checking a number of parameters among these is the torque.
Though with the current OEM software it might not as aggressive as some potential buyers would like. This will change for cars like the RS3.
A partly electrical system does not have to behave less effective than a 100% mechanical.

Your claim that it does transfer 90% of 335lb ft through the front wheels is simply not true. While it might be something like 100/0 or 90/10 when cruising the highway, it instantly changes those numbers well before you reach anywhere near 335lb ft engine output.

[clam]

Originally posted by DanielT
I think you need to study the Haldex design and application some more before you question it. Sure, it uses the axel speed difference (slip) to build oilpressure but it does prevent slip by checking a number of parameters among these is the torque.
Though with the current OEM software it might not as aggressive as some potential buyers would like. This will change for cars like the RS3.
A partly electrical system does not have to behave less effective than a 100% mechanical.

Your claim that it does transfer 90% of 335lb ft through the front wheels is simply not true. While it might be something like 100/0 or 90/10 when cruising the highway, it instantly changes those numbers well before you reach anywhere near 335lb ft engine output.

4WD/AWD is only usefull in situations with low grip. And Haldex only reacts to the loss of grip, so actually doesn't improve grip. And making it "more aggressive" can't fix this.

What I say is backed up in practice. The Haldex cars are slower than their FWD counterparts. B/c of the weight mainly. It doesn't improve performance, which is the only purpose of a 4WD system. The competition, FWD, RWD and real AWD alike, runs circles around the Haldex cars. Noone in their right mind would ever call an S60R, or R32, or TTq,... a sportscar.
So it fails to be a useful technology.

So what does it do? It evens out the weight distribution so VAG can put heavyweight engines like the VR6 in a FWD chassis.
And I suppose it can also act like a safety system, when you put big engines into small FWD cars. But there are many such systems out there that don't weigh/cost as much, like ESP.

But the real purpose of Haldex is a cynical marketing exercise, that allows companies to bank on the popularity AWD, without paying the cost. It is inferior to both FWD and real AWD.
It's sort of like the myth of SUVs being safer. Or minivans being more practical. As long as people buy it, they will make it. Even if it's BS.

If you know how Haldex works, then try this:
The function of a center differential in an AWD system is the same as a regular axle differential. So if Haldex is deemed a worthy replacement for a center diff, it should be the same for an axle diff.
Imagine replacing the regular differential of a car with a Haldex clutch. The left wheel for instance would get 90% of power most of the time. And each time it looses traction, the right wheel would get a little more power. How would it perform do you think?
And if the right wheel looses traction, then, well you're F-ed.
The car also wouldn't be able to make any left turns, b/c the distribution is limited to 50/50 (in a left turn, the right wheel has to get more than 50%).
Do you see how Hadex doesn't makes sense?

BTW, the 50/50 distribution in Haldex is only theoretical. In practice it can't run this, b/c then it would be able to compensate for differences in slip angle. It would be like running no differential at all.

RS3 rumour:
"quattro four-wheel drive utilizing the new and improved Haldex allowing unlimited power spit between driven wheels"
http://www.audi-sport.co.uk/rs3.html

[Nordschleife]

be very careful about slagging off what you call 'Haldex'. There is more than one version. The latest version is a closed loop system and much superior to previous versions.
I have found the latest Haldex system to work acceptably in snow.

R+C

[DanielT]

Originally posted by clam
4WD/AWD is only usefull in situations with low grip. And Haldex only reacts to the loss of grip, so actually doesn't improve grip. And making it "more aggressive" can't fix this.

What I say is backed up in practice. The Haldex cars are slower than their FWD counterparts. B/c of the weight mainly. It doesn't improve performance, which is the only purpose of a 4WD system. The competition, FWD, RWD and real AWD alike, runs circles around the Haldex cars. Noone in their right mind would ever call an S60R, or R32, or TTq,... a sportscar.
So it fails to be a useful technology.

So what does it do? It evens out the weight distribution so VAG can put heavyweight engines like the VR6 in a FWD chassis.
And I suppose it can also act like a safety system, when you put big engines into small FWD cars. But there are many such systems out there that don't weigh/cost as much, like ESP.

But the real purpose of Haldex is a cynical marketing exercise, that allows companies to bank on the popularity AWD, without paying the cost. It is inferior to both FWD and real AWD.
It's sort of like the myth of SUVs being safer. Or minivans being more practical. As long as people buy it, they will make it. Even if it's BS.

If you know how Haldex works, then try this:
The function of a center differential in an AWD system is the same as a regular axle differential. So if Haldex is deemed a worthy replacement for a center diff, it should be the same for an axle diff.
Imagine replacing the regular differential of a car with a Haldex clutch. The left wheel for instance would get 90% of power most of the time. And each time it looses traction, the right wheel would get a little more power. How would it perform do you think?
And if the right wheel looses traction, then, well you're F-ed.
The car also wouldn't be able to make any left turns, b/c the distribution is limited to 50/50 (in a left turn, the right wheel has to get more than 50%).
Do you see how Hadex doesn't makes sense?

BTW, the 50/50 distribution in Haldex is only theoretical. In practice it can't run this, b/c then it would be able to compensate for differences in slip angle. It would be like running no differential at all.

Funny thing that you'ld write such a long message about something that you obviously do not have a clue about.
I have a hard time finding anything at all in your piece that is correct information.

Interessting that you claim that other AWD systems runs circles around the "weight distributed" cars.
Really strange thing that one of these crappy cars pretending to be AWD easily outruns a torsen RS4 on a frozen lake track.
Similar ICE-stud tires, not much difference in driver capacity, RS4 550+hp, Haldex car 300-350hp. Weight difference something like 100-150kg.
This weight distributed car also runs equal times to Imprezas with plenty more power, but considerably less weight.

[DanielT]

Originally posted by clam
RS3 rumour:
"quattro four-wheel drive utilizing the new and improved Haldex allowing unlimited power spit between driven wheels"
http://www.audi-sport.co.uk/rs3.html

Please buy one and you will see that it do not behave that much different from the first generation Haldex units.
Some of the new haldex versions can create oil pressure without wheelslip, that way it can lock before any wheelslip. The current versions in VAG cars must use accumulated pressure or wait a couple of tenths. But ofcourse they'll be using more advanced software and therefore create slightly more aggressive feel. (which is also possible on todays cars)