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torsen diffs? vs lsd
daniel mason - 21/7/10 at 06:04 PM

can someone please explain the term 'torsen' diff (sorry if i spelt it wrong) and explain how it differs from an lsd? cheers

hobbsy - 21/7/10 at 06:16 PM

Torsen = TORque SENsing and is a type of LSD.

Other types of LSD's (like what you're probably referring to) are:

Viscous (like a Sierra 4x4 rear)
Plate / Clutch type

Torsen diffs use gears.

Check the quaife site for a better explanation than I can give.

Or just read:

http://en.wikipedia.org/wiki/Limited_slip_differential

SeaBass - 21/7/10 at 06:17 PM

All about Torsen / Torque Sensing

hobbsy - 21/7/10 at 06:23 PM

Heheh I always forget about LMGTFY!

Maybe I should send myself a link:

http://www.lmgtfy.com/?q=let+me+google+that+for+you

But I need to be careful I could end up in an infinite loop! heheh

[Edited on 21/7/10 by hobbsy]

Litemoth - 21/7/10 at 06:29 PM

My understanding is that an LSD allows a certain amount of slip (difference in rotational speed beween the two wheels across an axle) whereas the Torque Sensing option does it by sensing the resistance to movement and sending the power to the wheels in proportion to the resistance to turning 'felt' on that wheen (i.e. most grip)

It seems that they have a different handling & grip characteristic for the driver. The torsen is permanently engaged is smooth and gradual whereas the LSD 'switches' in when you have reached the 'limit' of the slip.

Wish I still had my Hillier and Pittuck book - those chaps explain it so much betterer



[Edited on 21/7/10 by Litemoth]

turbodisplay - 21/7/10 at 07:13 PM

The only dowside to torsen is that if there is no torque one one wheel (ice patch) the other wheel will have no torque.
Torsen requires some torque in the lower grip, and sends a multiple (about 5x) to the other wheel.
If there is no torque on one wheel the other gets 5 x 0 = 0.

Darren

v8kid - 21/7/10 at 07:22 PM

Hey Darren thats the best description of a Torsen diff I have heard - got it in a nutshell and thats just the way it works in practice 5*0=0 but 5* a bit is a lot more!

snapper - 21/7/10 at 08:46 PM

Reading the Wiki gave a trick you can use which is to apply the handbrake which will cause drag to the free spinning wheel therefor allowing the TorSen to load torque to the wheels

hobbsy - 21/7/10 at 08:55 PM

Snapper - good tip if you're on ice but no so good if you're riding kerbs on a trackday and the wheel is leaving the ground.

Generally I'd say the Quaife ATB (torsen) is the best but then I'm biased as I have one in my car

Its also a lot more money than fitting a vLSD from a 4x4 Sierra.

Neville Jones - 21/7/10 at 09:12 PM

quote:
Originally posted by turbodisplay
The only dowside to torsen is that if there is no torque one one wheel (ice patch) the other wheel will have no torque.
Torsen requires some torque in the lower grip, and sends a multiple (about 5x) to the other wheel.

If there is no torque on one wheel the other gets 5 x 0 = 0.

Darren


Absolutely untrue!! And back to front in thinking. The torque split is the the input torque being split, NOT the road grip. On ice, both wheels would get similar torque. Your thinking would have the diff not driving the axles at all, and the pinion spinning out of control. Think about it.

When both wheels have similar grip, they get similar torque. When one loses grip, the torque is split between BOTH wheels in the inbuilt ratio.

The torque split helps turn the car in corners. If you are doing a lot of tight cornering, you need a high torque split ratio. Big ovals, you need a more even torque split ratio.

The torque split ratio is dictated by the inbuilt gearing ratio, and can be altered in genuine Torsen diffs by Gleeson.

I've worked with these things for far too long.

And a Quaiffe diff is not a Torsen, but looks similar internally, and is a rudimentary attempt to circumvent a very robust patent.

Cheers,
Nev.

Liam - 21/7/10 at 10:59 PM

quote:

Absolutely untrue!! And back to front in thinking. The torque split is the the input torque being split, NOT the road grip. On ice, both wheels would get similar torque.


He said one wheel on ice, i.e one wheel with no grip, essentially the same situation as one wheel in the air. In which case a Torsen diff behaves ilke an open dif and spins the wheel with no grip away.

quote:

Your thinking would have the diff not driving the axles at all, and the pinion spinning out of control. Think about it.


As above - it is behaving like an open diff spinning the wheel with no grip and putting 0 torque to the ground through the wheel with grip.

I ought to say I've never used one, but everything I've ever read or heard about Torsens reports that limitation. That and the fact there are techiques developed to escape from that very situation by applying some drag to the wheel with no grip/in the air with the brakes/handbrake so that the diff can apply that drag x the bias ratio to the good wheel, gives me little doubt the situation is real.

But maybe you're right and everyone else is wrong?

jeffw - 22/7/10 at 05:50 AM

The Audi Quattro system uses Torsen diffs in the centre and, on some cars, the rear diff (note the A3 platform uses the Haldex system and is quattro not Quattro in Audi speak). I've had, the past 7 years, a 440BHP Audi B5 S4, 550BHP B5 RS4 and currently a 300BHP A6 3.0TDi and I can safely say I have never had the situation described above. I've used the cars on snow & ice and trackdays.

[Edited on 22/7/10 by jeffw]

v8kid - 22/7/10 at 06:05 AM

Nev my MX5 and TR8 both have quaiffe diffs and are 5ite in snow with one wheel spinning at the slightest provocation. Aided and abetted no doubt by the weight distribution nonetheless in practice it mirrors the description given by Darren where there is a point where the diff fails to allocate the drive between both wheels resulting in the pinions and one drive shaft spinning out of control.
Not sure how this is back to front thinking?

Neville Jones - 22/7/10 at 09:09 AM

A Quaiffe is NOT a Torsen, as I pointed out. A proper Torsen will ALWAYS give drive to the wheel with most grip. Mechanically impossible to do otherwise.

The Audi has proper genuine Torsen diffs, so no probs.

Don't ever try jacking up one corner of a car with a proper Torsen diff to check if it works, by applying power with one wheel in the air. The car WILL jump off the jack. A Quaiffe will spin up the free wheel, more often than not, as it relies on the lower grip wheel to apply some resistance so that the internal gears can grab on the housing. A Torsen operates very differently to a Quaiffe.

Cheers,
Nev.



[Edited on 22/7/10 by Neville Jones]

Liam - 5/8/10 at 08:46 PM

Stumbled on this video and thought of this thead .

Torsen diff (centre in this case) behaving as an open when one output can support no torque...

http://www.youtube.com/watch?v=Oo9GV4mSnRQ

Apparently that's 'mechanically impossible'. Fake vid i guess, then