RE: Haldex - the truth!
Discussion
Max_Torque said:
Front Longitudinal, rwd:
Front Transverse, 4wd
Front Longitudinal, 4wd
Off topic, but interesting to note that picture 1 has the engine blockFront Transverse, 4wd
Front Longitudinal, 4wd
over the front wheels, while pic 2 and pic 3 have it well forward
of the front wheels. Typical Audi ?
IIRC, A level Maths many decades ago, polar moment of inertia
says car in pic 1 is better balanced.
MiguelY said:
This article leaves out the Honda/Acura SH-AWD system that is unique and very cool. Extraordinary levels of traction and efficiency. But it also has torque vectoring to the rear wheels left and right to rotate the car, RWD car behavior. At the limit you can correct understeer with throttle.
Correct, and those jammy feckless in the states even got a manual box to go with it, http://www.roadandtrack.com/new-cars/road-tests/re...
The Ford's new system is in effect much like Honda's Shawd, but honda have now gone the electric route with torque vectoring, e-Shawd
http://www.roadandtrack.com/new-cars/road-tests/re...
Japan gets this now in the new Legend
http://www.honda.co.jp/LEGEND/
Corkman said:
"...Ford claims 70 per cent for its new Focus RS (not confirmed as Haldex, but likely)..."
"...The most famous recent convert is the Ford Focus RS, which has GKN's Twinster system coupled to the all-wheel drive set-up..."
erm.... ok.... I'm confused....
Yea I caught this too.. I'm not sure if Twister is a torque vectoring solution though? Wasn't explicitly clear to be honest..."...The most famous recent convert is the Ford Focus RS, which has GKN's Twinster system coupled to the all-wheel drive set-up..."
erm.... ok.... I'm confused....
RE: The abomination that is the 2 series active tourer: I think we're all still pretty horrified. I think BMW should have continued with the b
dization of the Mini brand rather than giving their own brand a stonking anal session. Disappoints me that BMW seem to be shirking their old image for a corporate one that chases money; don't get me wrong, i see why, but it's sad none the less.Zad said:
Interesting that the Sierra XR4x4 / Cosworth transmission pushed the engine further back (looking at this, maybe a metre or so relative to Audi) with the front half shaft going through the sump.
And the front prop occasionally going through the side of the gearbox 
Never ignore the knocking.Konan said:
And the front prop occasionally going through the side of the gearbox Never ignore the knocking.
Been there. Never ignore the knocking.
Decelerating off the motorway, I opened my mucky drivers window to get a good look at the roundabout traffic. Heard a tingtingtingtingtingtingting ting ting ting ting ting ting noise as I slowed down. Being an amazingly perceptive engineer, I thought: ello, that's not quite right. But drove home a couple of miles anyway. Gave it a good looking at and discovered the transfer shaft was not quite up to spec. Specifically, several of the UJ bearings had seized/collapsed and were merrily hacking their way through the housing in an attempt to set the shaft free to thrash around at high speed. Rather glad I noticed that really.
If I had a transverse engine and had to choose between a Subaru/Mitsu system or Haldex. It would be the japs every time.
Haldex does have it's benefits in a economical view point but for performance the full time systems are just better. A Proactive system is always going to be better than a Reactive system.
Haldex does have it's benefits in a economical view point but for performance the full time systems are just better. A Proactive system is always going to be better than a Reactive system.
cerb4.5lee said:
Hooli said:
I really don't understand all this technology being used to cure the basic fault that the cars should be RWD with a Haldex feeding some power to the front as needed.
kambites said:
BricktopST205 said:
If I had a transverse engine and had to choose between a Subaru/Mitsu system or Haldex. It would be the japs every time.
Subaru have a transverse 4wd system? That I didn't know, what's it used in? Mr Whippy said:
Today the Quattro is just a marketing thing, and to make it work at all they need to actually have four driven wheels.
Huh? They do make systems with full time AWD.Wikipedia said:
Quattro generation V
Starting with the B7 Audi RS4 and the manual transmission version of the 2006 B7 Audi S4. It was adopted in the entire S4 lineup in 2007.[1] and become the standard fitment on all quattro Audis with longitudinal engine layout until replaced in the 2010 RS5.
System type: Permanent asymmetric four-wheel drive.
Torsen type 3 (Type "C") centre differential, 40:60 'default' split front-rear, automatically apportioning up to 80% of the torque to one axle using a 4:1 high-biased center differential. With the aid of ESP, up to 100% of the torque can be transferred to one axle.
Starting with the B7 Audi RS4 and the manual transmission version of the 2006 B7 Audi S4. It was adopted in the entire S4 lineup in 2007.[1] and become the standard fitment on all quattro Audis with longitudinal engine layout until replaced in the 2010 RS5.
System type: Permanent asymmetric four-wheel drive.
Torsen type 3 (Type "C") centre differential, 40:60 'default' split front-rear, automatically apportioning up to 80% of the torque to one axle using a 4:1 high-biased center differential. With the aid of ESP, up to 100% of the torque can be transferred to one axle.
Catatafish said:
kambites said:
BricktopST205 said:
If I had a transverse engine and had to choose between a Subaru/Mitsu system or Haldex. It would be the japs every time.
Subaru have a transverse 4wd system? That I didn't know, what's it used in? kambites said:
Most 4wd Audis aren't transverse engined. Although obviously most of the Haldex ones are. 
Unfortunately even the longitudinal engined ones have the engine rather a long way forward. I'm not convinced that's the primary cause of their rather front-lead chassis balance though. I suspect they do that because Audi want them to do that. It's easy enough to get a front weight biased car to oversteer by playing with the suspension setup if you want it to.
If you look at Audi's over time they have worked hard to get the engine as far back as they can.Unfortunately even the longitudinal engined ones have the engine rather a long way forward. I'm not convinced that's the primary cause of their rather front-lead chassis balance though. I suspect they do that because Audi want them to do that. It's easy enough to get a front weight biased car to oversteer by playing with the suspension setup if you want it to.
Just look at the older 01E gearbox
vs the latest one
They've moved the drive shafts as far forwards as they can to try and kill the understeer from hanging that engine way out in front.
Despite what BMW may claim 50:50 is not the ideal, (although it's a very good start for anything front engined), something like 30:70-40:60 would be better as the inertia from trying to change the direction of the big lump up front causes understeer (and that is one of the [many] reasons I dislike diesels with their big heavy engines). Almost impossible for anything that's not rear engined though.
Might find this interesting as well, a list of the more common "AWD" systems and how they all work:
http://www.cnet.com/pictures/all-wheel-drive-syste...
http://www.cnet.com/pictures/all-wheel-drive-syste...
The enhancement that a good AWD system gives to it's 2WD counterpart is the reduced tractive force on the tyres that would be normally doing all the work, making the other two share the load.
That way, the number of times that you actually exceed the level of available traction will be generally reduced, and the amount of power reduction you have to have to make the tyres grip again is reduced.
Haldex systems deal with the loss of grip on the normally driven wheels by channeling power to the other two by activating a clutch which for the average person trying to cross a wet field or move along a snowy road is perfectly adequate.
The art is in the calibration of the clutch actuation. If the clutches are mostly disengaged, the transition the car makes as tractive grip is lost and restored will be pretty abrupt.
If the clutches are mostly on and making minor adjustments in tractive force to each axle, the transitions will be far less abrupt.
The devil is in the details.
That way, the number of times that you actually exceed the level of available traction will be generally reduced, and the amount of power reduction you have to have to make the tyres grip again is reduced.
Haldex systems deal with the loss of grip on the normally driven wheels by channeling power to the other two by activating a clutch which for the average person trying to cross a wet field or move along a snowy road is perfectly adequate.
The art is in the calibration of the clutch actuation. If the clutches are mostly disengaged, the transition the car makes as tractive grip is lost and restored will be pretty abrupt.
If the clutches are mostly on and making minor adjustments in tractive force to each axle, the transitions will be far less abrupt.
The devil is in the details.
James72911 said:
Interesting comments - I thought the article was very interesting, and gave some useful insight into the subject... Good to see a more techy piece along with the regular reviews.
While I agree entirely, I would also say that it's not exactly enlightening independent journalism. Mostly a load of quotes from professional salespeople and PR men. No offence to the writer or PH and I'm glad to see the efforts.A great deal more has been learnt from the idle follow-ups of members than the original article. I'm glad for the efforts but I hope PH can aim to build up from this for future articles.
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