AWD Systems (from Overrated...)

[KoRnJD]

Originally posted by 4wheeldrift
But the Skyline IS NOT using TorSen differentials. The skyline is using a fully computer controlled, bias adjustable differentials, similar to the active diffs on a WRC car, that is not prone to this weakness. This is why the AWD system on the skyline is superior to the quattro system, regardless of how much torque is being transferred where (and theoretically, since the system is fully computer controlled you could tell it to route 100% of the power to one drive wheel, if the system was programmed to allow it). A TorSen still requires a bit of slippage (this is why the gears mesh, because the wheels are turning at different speeds indicating that one wheel is slipping), so it reacts more quickly to changes in surface than a conventional Viscous Coupling differential, but the time for a TorSen to take full effect and a computer controlled diff to do the same thing are very similar.

At any rate, the amount of computer control and integration with other systems is what makes the skylines all wheel drive system one of the most advanced avaiable on a road car. It doesn't necessarily work any better than mechanical LSDs at each end, but IT IS a lot more advanced.

Oh, I see.

But, I was always taught that 4M/Quattro sensed slip before it occurred, thus being proactive. Any thoughts?

The Skyline's system sounds sweet. I tried looking for sources of info describing how it works in detail, but to no avail. Does anyone know where to find a document like this?

Thanks!

[4wheeldrift]

Originally posted by KoRnJD


Oh, I see.

But, I was always taught that 4M/Quattro sensed slip before it occurred, thus being proactive. Any thoughts?

The Skyline's system sounds sweet. I tried looking for sources of info describing how it works in detail, but to no avail. Does anyone know where to find a document like this?

Thanks!

Proactive vs Reactive is simply a question of how long it takes the system to react. The TorSen is reacting to differences in frictional forces on the gears inside it to transfer power. Its normally locked at 50/50 split (each wheel gets its own share of the power), but it has no way of knowing the road 100 metres ahead of you is going right to hell, from a traction perspective. Its reacting to the change in traction as its occuring, instead of after a wheel has already slipped, which is what makes it by definition "proactive", as opposed to a system like a Viscous Coupling which is "reactive" since slipping has already occured when it changes torque bias. There still has to be some slippage for the TorSen to change its power settings, because without a change in rotational speed (even a very minute one) of the two axles it has no way of knowing its losing traction. The computer controlled system in the Skyline does the same thing, except it is sensing differences in wheel speed to determine something is amiss. It reacts the same way as a TorSen, in that the computer sees one wheel is starting to lose traction and adjusts things accordingly.

[Mikko]

As far as I understood 4WD systems, none of them can sense slip before it occurs. They all just have longer or shorter reaction times.

Lancer Evo VII has a actice central differential made up of a computer controlled multi-plate clutch. It has tons of advantages, including the ability to disconnect when using the handbrake for hairpins - marvelous! The only AWD road car to have such a feature. Porsche 959 was first with the active diffs though.

[DSM Power]

How is AWD overrated?!

Edit - I see it now....

[KoRnJD]

Originally posted by 4wheeldrift
...it has no way of knowing the road 100 metres ahead of you is going right to hell, from a traction perspective.

LMAO!

Stupid me...

Of course.

So, in the Skyline, the computer senses that one wheel is losing traction, and retracts power from that wheel to send it to the other ones? So does that mean that there are 3 multi-plate clutches (or equivalent) on the car (one for front to rear, and one for each axle)?

Do we have diagrams? (I'm a visual learner...)

[Hipermax_d]

Originally posted by KoRnJD
The Skyline's system sounds sweet. I tried looking for sources of info describing how it works in detail, but to no avail. Does anyone know where to find a document like this?

Thanks!

ill scan you my skyline brochure but i cant read most of the words

[4wheeldrift]

Originally posted by KoRnJD


LMAO!

Stupid me...

Of course.

This is why i hate seeing the advertisements for TorSen equipped cars, because it makes it seem like its some sort of miracle diff that can tell you are going to have problems before you ever hit that black ice, or what have you.

Originally posted by KoRnJD
So, in the Skyline, the computer senses that one wheel is losing traction, and retracts power from that wheel to send it to the other ones? So does that mean that there are 3 multi-plate clutches (or equivalent) on the car (one for front to rear, and one for each axle)?

The Skyline uses a computer controlled center helical diff, and clutch type front and rear diffs. All of the diffs are hydraulically controlled by the cars all wheel drive control computer so they can change the torque bias in any direction as soon as the computer starts to detect a loss of traction through the sensors at each wheel, as well as manipulating the brakes like a traditional traction control system (since the all wheel drive system is integrated with the ABS system, a yaw control system and traction control).

[KoRnJD]

Originally posted by 4wheeldrift
The Skyline uses a computer controlled center helical diff, and clutch type front and rear diffs. All of the diffs are hydraulically controlled by the cars all wheel drive control computer so they can change the torque bias in any direction as soon as the computer starts to detect a loss of traction through the sensors at each wheel, as well as manipulating the brakes like a traditional traction control system (since the all wheel drive system is integrated with the ABS system, a yaw control system and traction control).

Very cool. Thanks for the explanation!

[Fuji]

Originally posted by Mikko
As far as I understood 4WD systems, none of them can sense slip before it occurs. They all just have longer or shorter reaction times.

Lancer Evo VII has a actice central differential made up of a computer controlled multi-plate clutch. It has tons of advantages, including the ability to disconnect when using the handbrake for hairpins - marvelous! The only AWD road car to have such a feature. Porsche 959 was first with the active diffs though.

Ummm I don't think any road cars get that system.... Anyways the clutch packs are toast after 15000 kms at best... it is a good system if you have $$$ and a team of mechanics at hand.

[Mikko]

Both Porsche 959 and Lancer Evo VII GSR has it. Active center diff and AYC rear. The front diff is of torsen type. They may toast but it still has the center active diff.

[szw]

I remember reading about some wrx that had that feature (handbrake disables the awd system). either an STi or WRC car, forget which.

[4wheeldrift]

Originally posted by szw
I remember reading about some wrx that had that feature (handbrake disables the awd system). either an STi or WRC car, forget which.

its the WRC machine, because the STi doesn't have anything resembling active diffs.

[XylathaneGTR]

Yeah, i saw that on Speed Channel a while ago...
It was some random thing, but it was a HUGE ass explination and breakdown of the WRC cars, i saw the subaru, was the last one. But yeah, when the handbrake is engaged, it cuts off the rear wheels for quick ass harpin turns and stuff.
I know in the GTR32's and GTR34's You can just remove a fuse or 2 and it totally disables the Front differential and everything, so all power is sent to the rear wheels (usefull for dynoing) On the GTR33, it gets trickier tho, and u sometimes have to remove the axel etc.

Some of the technology thats in place in some cars today is mindblowing...

[Mikko]

Originally posted by 4wheeldrift
its the WRC machine, because the STi doesn't have anything resembling active diffs.

What are you getting on the new STi? I think it might actually be an active diff. From what I read so far, it has either manual mode with two thirds of the power rear, or 50/50, or automatic mode where the computer varies...something, can't remember if it's the limited slip or the torque split.

[4wheeldrift]

Originally posted by Mikko


What are you getting on the new STi? I think it might actually be an active diff. From what I read so far, it has either manual mode with two thirds of the power rear, or 50/50, or automatic mode where the computer varies...something, can't remember if it's the limited slip or the torque split.

"Active" differentials are fully computer controlled. The STi that is coming to north america has a driver adjustable diff that allows you to change the torque bias, but the driver has to do it manually, and you can only go from 35/65 to 50/50. There is no computer control on the center diff in the STi.

[Alpine Autowerks]

I've done some surfing on the subject and someone compared the Skyline system to the first gen. MB 4-matic system. I found a power path diagram for the R33 that confirms this. I took the MB course on the 4-Matic and it looks the same mechanically minus a steering wheel angle sensor used on the Benz to model the drivers intended course.

These are NOT AWD systems! It is a rear wheel drive system with part time AWD via a hydraulically applied clutch.

The rear diff is either open or locked (up to the torque limit of the clutch plates) called 50/50. Power is not "directed" but the clutches force the wheels to rotate at the same speed regardless of their traction. When the diff is open power travels to the wheel with the least amount of traction.

The center diff (when engaged) is first open (not locked) with a torque split from a planetary gear set. This gives the ~35/65 torque split. The computer can then lock the elements of the planetary gears. This forces the front and rear axles to rotate at the same speed. This is the 50/50 torque split.

There is no steady state torque split other that the values I have mentioned. The torque can be in-between as the clutches are locking or unlocking.

A lot of people mention the 959 as a high water mark as well. It is in the top to be sure. It used a neat trick to get more torque to the front so that it could pull out of an excessively large slide. The front tires had a larger circumference than the rears so when the centre clutch (no centre diff) was progressively locked to the rears it effectively sent more power (it was actually speed) to the front.

The Porsche 964 (1989-1994 911) was more advanced than the 959 (I was on the training course for those too) and gets my vote for the best AWD system ever.

[4wheeldrift]

The all wheel drive system in the 959 is the closest to true, WRC style active diffs seen in a street vehicle to date. You've managed to find a lot better information than I have, the technical details I've seen have all said that the Skyline's system stated it was able to manipulate the amount of torque sent to the different wheels and ends of the car in variable degrees. Thanks for an excellent explanation.

[KoRnJD]

Originally posted by Alpine Autowerks
A lot of people mention the 959 as a high water mark as well. It is in the top to be sure. It used a neat trick to get more torque to the front so that it could pull out of an excessively large slide. The front tires had a larger circumference than the rears so when the centre clutch (no centre diff) was progressively locked to the rears it effectively sent more power (it was actually speed) to the front.

The Porsche 964 (1989-1994 911) was more advanced than the 959 (I was on the training course for those too) and gets my vote for the best AWD system ever.

So, in your opinion, how does a Torsen system rate (in the A4 & Passat)?

P.S. Thanks for the detailed expo...

[Mikko]

I think the Torsen LSD is the ideal LSD for a road car built to last. Those old Ur Quattros from the 80's still have it running strong.

[Alpine Autowerks]

Originally posted by 4wheeldrift
The all wheel drive system in the 959 is the closest to true, WRC style active diffs seen in a street vehicle to date. .

The 964 has an active diff as does the 928 GTS and it was an option on 993 C2's. The software is not as complex as the WRX race equip, but the hardware is equivalent. The 959 req'd the drive to select a tracion mode due to the limits of early 80's computers, the 964 had 32 bit cpu & multiple traction maps. and 2 actively controlled (centre & rear) diffs with intergrated ABS. The 959 had 1 active diff, and standalone WABCO ABS.



The torsen is great.