Is X drive the same as haldex
Discussion
Herman Toothrot said:
That's an interesting random fact. I always thought the X5 was slagged of for zero off road ability but never heard anyone say similar of Range Rovers.
If you want to go off-road, you don't need this electronic torque vectoring crap. You need:- A locking centre differential. Locking as in regardless of traction on any wheel, the output prop shaft to the front axle turns at the same speed as to the rear axle as they are rigidly connected by the locked centre differential.
- Low range gears
- You can add locking rear or locking front and rear differentials if you want to get out of even trickier situations
Despite all the electronic crap, a Range Rover still has a locking centre differential and low range. That's what you need to go offroad.
It can be done in an X5 though, see here:
http://www.youtube.com/watch?v=pSWF5Tdc9Iw
The bits where diagonally opposite wheels end up off the ground (4:10 in the vid), even an older Range Rover with open front and rear differentials and no electronic gadgets, would get stuck.
creampuff said:
If you want to go off-road, you don't need this electronic torque vectoring crap. You need:
- A locking centre differential. Locking as in regardless of traction on any wheel, the output prop shaft to the front axle turns at the same speed as to the rear axle as they are rigidly connected by the locked centre differential.
- Low range gears
- You can add locking rear or locking front and rear differentials if you want to get out of even trickier situations
Need?- A locking centre differential. Locking as in regardless of traction on any wheel, the output prop shaft to the front axle turns at the same speed as to the rear axle as they are rigidly connected by the locked centre differential.
- Low range gears
- You can add locking rear or locking front and rear differentials if you want to get out of even trickier situations
I've spent time in a Defender with 2 of the 3 above (plus electronic traction control trickery) at the LR off road centres, the Freelander which doesn't have any of the above definitely followed us around all day.......off road. I suspect an Audi A4/6/8/whatever with torsen Quattro or 3 series Xdrive may not have.
Doesn't NEED.
Scuffers said:
Except it's just marketing speak...
Haldex is a clutch, and as such, cannot torque split as such, all it can do is join the front and rear axles together (with a variable degree of slip toothed rear)
A differential can deal with front and rear axles at different speeds
To try claim otherwise is just showing mechanical ignorance.
What I posted is how the thing works, nothing to do with marketing.Haldex is a clutch, and as such, cannot torque split as such, all it can do is join the front and rear axles together (with a variable degree of slip toothed rear)
A differential can deal with front and rear axles at different speeds
To try claim otherwise is just showing mechanical ignorance.
Edited by Scuffers on Tuesday 11th February 19:37
The 50/50 differential splits torque equally to both axles and on slip transfers power to the front or rear as needed (and can do up to 75% to the rear).
Haldex 4 and 5 prelock the clutch pack at 50/50 and then transfer torque as needed based on slip (and can do up to 100% to the rear).
Hence the Haldex functions like the old Torsen on the road in the conditions where it is needed. And it reacts faster and can send more torque to a given axle.
Your response is that it is not a differential. Correct, a clutch pack is not a differential.
creampuff said:
Even if it is a clutch, if the clutch is fully engaged and both axles are on the same surface, then there will be a 50:50 torque split (or however it is geared). It will remain 50:50 with an engaged clutch unless one axle is on mush in which case that axle will get (about) 0% of the torque and the other axle will get 100%.
This is mostly correct, except that there is no need to use "mush" or "ice" as an example in which Haldex would be predominantly rear driven. In sports oriented driving, this happens even on a surface where both axles have good grip, as the front axle always generates some slip on acceleration (due to dynamic weight transfer) and duing cornering (due to the path the front wheels take vs. the rears). What Haldex cannot do is *overdrive* the rear axle. But Audi's Torsens did not do that either until recently, when they altered the gearing in the diff to allow mechanical lockup of 40/60 (the diffs base split). But even this set up still behaves very similarly to a modern Haldex or 50/50 Torsen.
The optional sports diff goes further and uses torque vectoring to take advantage of the slight rear bias on the new center diff config. -- allowing a marginal amount of power oversteer under extreme provocation. But, generally, neutrality, grip, and stability up to the limit are the characteristics of these systems. If you want something with heavy rear bias, you are better off with a pure RWD car, as you begin to lose the stability and grip vs a system with a more even power distribution. 40/60 has historically been considered to offer the best compromise of traction, grip, balance, and stability.
Edited by scherzkeks on Saturday 15th February 11:10
scherzkeks said:
What I posted is how the thing works, nothing to do with marketing.
The 50/50 differential splits torque equally to both axles and on slip transfers power to the front or rear as needed (and can do up to 75% to the rear).
Haldex 4 and 5 prelock the clutch pack at 50/50 and then transfer torque as needed based on slip (and can do up to 100% to the rear).
Hence the Haldex functions like the old Torsen on the road in the conditions where it is needed. And it reacts faster and can send more torque to a given axle.
Your response is that it is not a differential. Correct, a clutch pack is not a differential.
FFS this is hard work!The 50/50 differential splits torque equally to both axles and on slip transfers power to the front or rear as needed (and can do up to 75% to the rear).
Haldex 4 and 5 prelock the clutch pack at 50/50 and then transfer torque as needed based on slip (and can do up to 100% to the rear).
Hence the Haldex functions like the old Torsen on the road in the conditions where it is needed. And it reacts faster and can send more torque to a given axle.
Your response is that it is not a differential. Correct, a clutch pack is not a differential.
your 50/50 split is nothing of the sort, it's a solid shaft (once the clutch is closed), ie, it's not splitting anything, any resultant drive is by virtue of whatever each end is doing.
this is no different to how part-time systems of old work, ala. LandRovers of old that ran RWD with a 'clutch' (Dog) to engage the front propshaft, once engaged, you had 4WD with no centre diff, so your next issue is transmission wind-up, hence why you can't run one in 4WD on high grip surfaces without doing damage (quite apart from the adverse handling characteristics of not having a centre diff brings).
Later Landrovers then went with centre diffs so that they could run permanent 4wd, but still with a clutch to lock said diff if terrain demanded.
current trend is now is to have asymmetric centre diffs with clutch based LSD's usually electrically controlled (like X5's for example), or torsen LSD's, or even viscus coupling LSD's (Subaru's of old).
all these are centre diffs though just with different ways of implementing some kind of LSD functionality.
Haldex and the like are NOTHING LIKE THIS, it cannot replicate the functions of a diff (Torsen or otherwise.)
with the VW implementation, the front axle is 100% connected to the gearbox output no matter what, there is no ability to vary the speed of the front diff from the gearbox output.
the rear drive is taken from this and clutched, so the rear diff can never rotate at any speed faster than the front, only slower until the clutch drags the two together in much the same way the old part-time systems work, at which point, you have lockup, with no ability for the speed of each axle to vary relative to each other.
Now, this might be what you want at very low speeds on surfaces with limited grip (as in the off-roaders usual challenge) but on a road it's far from ideal as you will get transmission wind up causing one end to push/pull the other, this makes for some interesting handling to put it mildly, hence why they have to 'slip' the clutch as opposed to locking it.
once you at this point, your back to the front axle being driven faster and harder than the rear, with all the usual handling issues that brings.
Now, to the person that posted up the pic of the Lambo, yes, it mat well use the same name of clutch system, but think about it for a minute, it's the other way round, ie, the rear axle is 100% driven, and the front is dragged up to it by said clutch, thus preserving the RWD balance of the chassis (in much the same was as a few 4WD cars do, GTR, Veyron, 911, and even the Ferarri FF etc.) the other point here is that none of these at any point are designed (or even want) anything like 100% drive from the front.
Test driver said:
Haldex is often dismissed on pistonheads as inferior; usually by those who have never used it. Aftermarket upgrades are also available that alter the bias for better balance/dynamics but at the cost of fuel economy.
Haldex 4wd is far better than any fwd, and a lot of rwd setups; but you have to adapt your driving style to get the most from it.
Even if you can adapt your driving style, 'better' in an objective sense will only ever apply to specific situations that make up a small percentage of driving for most people. 'Better' for the majority if people, most of the time, is subjective. The huge variety of handling characteristics available with FWD, RWD and the various flavours of 4WD will always divide opinion and is highly subjective. Personally I've always preferred 2WD for road and track (ie hard surface) driving, with a strong preference towards RWD. I'm ok in snow etc and get by, but that 'getting by' means I can enjoy the other 99% of my driving on wet and dry roads with my chosen subjective preference.Haldex 4wd is far better than any fwd, and a lot of rwd setups; but you have to adapt your driving style to get the most from it.
Scuffers said:
scherzkeks said:
What I posted is how the thing works, nothing to do with marketing.
The 50/50 differential splits torque equally to both axles and on slip transfers power to the front or rear as needed (and can do up to 75% to the rear).
Haldex 4 and 5 prelock the clutch pack at 50/50 and then transfer torque as needed based on slip (and can do up to 100% to the rear).
Hence the Haldex functions like the old Torsen on the road in the conditions where it is needed. And it reacts faster and can send more torque to a given axle.
Your response is that it is not a differential. Correct, a clutch pack is not a differential.
FFS this is hard work!The 50/50 differential splits torque equally to both axles and on slip transfers power to the front or rear as needed (and can do up to 75% to the rear).
Haldex 4 and 5 prelock the clutch pack at 50/50 and then transfer torque as needed based on slip (and can do up to 100% to the rear).
Hence the Haldex functions like the old Torsen on the road in the conditions where it is needed. And it reacts faster and can send more torque to a given axle.
Your response is that it is not a differential. Correct, a clutch pack is not a differential.
your 50/50 split is nothing of the sort, it's a solid shaft (once the clutch is closed), ie, it's not splitting anything, any resultant drive is by virtue of whatever each end is doing.
this is no different to how part-time systems of old work, ala. LandRovers of old that ran RWD with a 'clutch' (Dog) to engage the front propshaft, once engaged, you had 4WD with no centre diff, so your next issue is transmission wind-up, hence why you can't run one in 4WD on high grip surfaces without doing damage (quite apart from the adverse handling characteristics of not having a centre diff brings).
Later Landrovers then went with centre diffs so that they could run permanent 4wd, but still with a clutch to lock said diff if terrain demanded.
current trend is now is to have asymmetric centre diffs with clutch based LSD's usually electrically controlled (like X5's for example), or torsen LSD's, or even viscus coupling LSD's (Subaru's of old).
all these are centre diffs though just with different ways of implementing some kind of LSD functionality.
Haldex and the like are NOTHING LIKE THIS, it cannot replicate the functions of a diff (Torsen or otherwise.)
with the VW implementation, the front axle is 100% connected to the gearbox output no matter what, there is no ability to vary the speed of the front diff from the gearbox output.
the rear drive is taken from this and clutched, so the rear diff can never rotate at any speed faster than the front, only slower until the clutch drags the two together in much the same way the old part-time systems work, at which point, you have lockup, with no ability for the speed of each axle to vary relative to each other.
Now, this might be what you want at very low speeds on surfaces with limited grip (as in the off-roaders usual challenge) but on a road it's far from ideal as you will get transmission wind up causing one end to push/pull the other, this makes for some interesting handling to put it mildly, hence why they have to 'slip' the clutch as opposed to locking it.
once you at this point, your back to the front axle being driven faster and harder than the rear, with all the usual handling issues that brings.
Now, to the person that posted up the pic of the Lambo, yes, it mat well use the same name of clutch system, but think about it for a minute, it's the other way round, ie, the rear axle is 100% driven, and the front is dragged up to it by said clutch, thus preserving the RWD balance of the chassis (in much the same was as a few 4WD cars do, GTR, Veyron, 911, and even the Ferarri FF etc.) the other point here is that none of these at any point are designed (or even want) anything like 100% drive from the front.
Now just to add to the mix - better for a road car still was Mazda epicyclic driven system centre diff arrangement (I Think Subaru are similar too) Allowed for different ratio diffs front & rear giving torque bias but allowed for speed differences front & rear whilst cornering. Add in VLSD on all axles & a superb mechanical system - just a shame they broke quite a lot.
As used in the Mazda 323 GT-R Homologated version & the GT-X & I think its the same system in the Mazda CX-7
Indeed, for true dynamic yaw control, an epicyclic overspeeding centre differential (EOCD) is needed, pioneered in the WRC and later fitted to cars such as the DCCD in the Impreza and AYC in the Evo.
If you understand what "yaw" actually is for a car, then perusal of the following graph should help you understand the importance of a speed bias and not a torque bias:
The reason a FWD Haldex car is not as "fun" or "good" to drive as a car with an EOCD is because all a haldex can do (as mentioned by previous posters) is maximise overall ongitudinal acceleration (ie traction) and not modulate lateral acceleration independently at each axle (ie yaw control)
If you understand what "yaw" actually is for a car, then perusal of the following graph should help you understand the importance of a speed bias and not a torque bias:
The reason a FWD Haldex car is not as "fun" or "good" to drive as a car with an EOCD is because all a haldex can do (as mentioned by previous posters) is maximise overall ongitudinal acceleration (ie traction) and not modulate lateral acceleration independently at each axle (ie yaw control)
Scuffers said:
FFS this is hard work!
your 50/50 split is nothing of the sort, it's a solid shaft (once the clutch is closed), ie, it's not splitting anything, any resultant drive is by virtue of whatever each end is doing.
this is no different to how part-time systems of old work, ala. LandRovers of old that ran RWD with a 'clutch' (Dog) to engage the front propshaft, once engaged, you had 4WD with no centre diff, so your next issue is transmission wind-up, hence why you can't run one in 4WD on high grip surfaces without doing damage (quite apart from the adverse handling characteristics of not having a centre diff brings).
The rear axle is always powered in a Haldex vehicle. Typically 15% is the norm for an Audi. Second, when the clutch pack is closed, there is still allowance for slip via the front diff/transaxle arrangement. If there were not, Haldex and VAG could not claim that it was possible to send more than 50% of torque rearward when the front axle has slip on it. We aren't talking about an off road vehicle here.your 50/50 split is nothing of the sort, it's a solid shaft (once the clutch is closed), ie, it's not splitting anything, any resultant drive is by virtue of whatever each end is doing.
this is no different to how part-time systems of old work, ala. LandRovers of old that ran RWD with a 'clutch' (Dog) to engage the front propshaft, once engaged, you had 4WD with no centre diff, so your next issue is transmission wind-up, hence why you can't run one in 4WD on high grip surfaces without doing damage (quite apart from the adverse handling characteristics of not having a centre diff brings).
The clutch pack in Gen. 4 and 5 is regulated by the ECU and (fully) locked as needed in agressive driving -- independent of slip. In a locked state, slip on an axle dictates that more torque is transferred to the slower axle. These are facts. It is also a fact that Haldex can and does regularly send more than 50% of torque to the rear axle.
What it cannot do is overdrive the axle, but neither can a Torsen 50/50. Both of these systems function very similarly. 50/50 lock up to ensure that "preemptive" torque is available for stability reasons (though Torsen is obviously in this mode at all times in absence of slip), and the ability to shift additional torque (up to 100% for Haldex and up to 85% for Torsen if the unit is a high-bias ratio version).
In order for a diff like Torsen to be capable of overdriving the rear, it's base configuration must be altered, hence the 40/60 static splits we see on newer versions.
And the latest Gen 4 and 5 Haldexes most certainly do emulate a diff. The entire purpose of developing the Pre-x tech. and then ultimately moving to independently driven pumps for the accumulator was to provide the system with the ability to have an even torque split available immediately when needed to aid stability and dynamics and give it the progressive feel it lacked in early versions on hard driving. This eliminated the "seesaw" effect of earlier versions, which were highly front-biased until a major slip event was detected, in which case the systems attempt to balance things by transferring torque rearward was abrupt and not nearly as progressive as the mechanical systems.
Edited by scherzkeks on Thursday 20th February 14:37
scherzkeks said:
The clutch pack in Gen. 4 and 5 is regulated by the ECU and (fully) locked as needed in agressive driving -- independent of slip. In a locked state, slip on an axle dictates that more torque is transferred to the slower axle. These are facts. It is also a fact that Haldex can and does regularly send more than 50% of torque to the rear axle.
once again, your not understanding the terminology.scherzkeks said:
What it cannot do is overdrive the axle, but neither can a Torsen 50/50. Both of these systems function very similarly. 50/50 lock up to ensure that "preemptive" torque is available for stability reasons (though Torsen is obviously in this mode at all times in absence of slip), and the ability to shift additional torque (up to 100% for Haldex and up to 85% for Torsen if the unit is a high-bias ratio version).
wrong, a differential can deal with the front and read drive running at different speeds, that's what it's called a differential, makes no odds if it's torsen/open/viscus/plated/etc. they are only ways of limiting the speed differential (and thus limiting the 'slip')scherzkeks said:
In order for a diff like Torsen to be capable of overdriving the rear, it's base configuration must be altered, hence the 40/60 static splits we see on newer versions.
wrong, your miss-understanding what an asymmetric diff is, once again, this is not a question of if it's torsen or not, it's about the design of the diff itself.what an asymmetric diff does is have a non-50/50 torque split, irrelevant of what the relative speeds are.
scherzkeks said:
And the latest Gen 4 and 5 Haldexes most certainly do emulate a diff. The entire purpose of developing the Pre-x tech. and then ultimately moving to independently driven pumps for the accumulator was to provide the system with the ability to have an even torque split available immediately when needed to aid stability and dynamics and give it the progressive feel it lacked in early versions on hard driving. This eliminated the "seesaw" effect of earlier versions, which were highly front-biased until a major slip event was detected, in which case the systems attempt to balance things by transferring torque rearward was abrupt and not nearly as progressive as the mechanical systems.
Look, you're tying yourself up in knots here, it's a clutch, no more, no less, and yes, with an independent oil pump and electronic control, it can be 'programmed' to act independent of shaft speeds etc. however, that does not mean it can suddenly mimic the functionality of a diff.if you want to look at an electronic clutch based differential, may I suggest you study the NV125 transfer case from a Range Rover/X5? this is a true asymmetric diff with a electrically controlled clutch pack to limit slip, this has the ability to provide torque to both axles at all times and still manage torque transfer when one axle looses grip, be that front or rear.
ie, the clutch pack only carries the transfer-torque, not the full drive to one end of the car
Torsen achieves the same function just in a purely mechanical fashion, and never get's to the point of being 'locked'.
for low-speed off-road tyre use, the NV125 clutched LSD is more controllable, on road in a 'sports car' type use, torsen is probably preferable.
Scuffers said:
once again, your not understanding the terminology.
Then explain. What terminology did I misunderstand with regard to that paragraph.Scuffers said:
wrong, a differential can deal with the front and read drive running at different speeds, that's what it's called a differential, makes no odds if it's torsen/open/viscus/plated/etc. they are only ways of limiting the speed differential (and thus limiting the 'slip')
The Torsen in question uses gearing to respond to differences in axle speed. Haldex uses electronics, first to effect clutch preemptive lockup and to detect slip to transfer proportional torque as needed. Both systems have the same goal: to transfer torque to the axle that has more grip. Scuffers said:
wrong, your miss-understanding what an asymmetric diff is, once again, this is not a question of if it's torsen or not, it's about the design of the diff itself.
We are not only discussing diffs setup to produce uneven static splits; I mentioned this several times. We are discussing the function of a Torsen-type diff vs. a Haldex. The Torsen and Haldex operate on slip. The Torsen can only overdrive an axle if the gearing is configured to allow a static torque split other than 50/50, otherwise it is doing what the Haldex is doing: managing axle speeds to restore traction. Scuffers said:
what an asymmetric diff does is have a non-50/50 torque split, irrelevant of what the relative speeds are.
Correct!Scuffers said:
Look, you're tying yourself up in knots here, it's a clutch, no more, no less, and yes, with an independent oil pump and electronic control, it can be 'programmed' to act independent of shaft speeds etc. however, that does not mean it can suddenly mimic the functionality of a diff.
Not at all. I am discussing how a Torsen 50/50 diff and a modern Haldex do essentially the same job on the road, but with different approaches. I see that you do -- despite claims to the contrary -- understand how preemptive locking with torque dist. on slip mimics a Torsen diff in function though. Cheers for that.Scuffers said:
ie, the clutch pack only carries the transfer-torque, not the full drive to one end of the car
What? Torque is the "drive" in question. A 50/50 Torsen operates in a "locked fashion" and distributes that way full-time. A Haldex with a locked clutch pack does the same, and for most is more effective as it only fully locks when needed, rather than at all times. Both operate on slip beyond that.Scuffers said:
Torsen achieves the same function just in a purely mechanical fashion, and never get's to the point of being 'locked'.
What? It is locked from the get-go in a static torque split. The point of upgrading the Haldex hardware was to give the system the same function when needed, as I already outlined. Both then operate on slip beyond that.
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