LSD noise when cold - normal?

[rice_classic]

This video from the same guy is a little better explaining the torque bias:
[ame="http://www.youtube.com/watch?v=lDsQAs0Ldes"]Torsen LSD - Torque Transfer - Explained - YouTube[/ame]

[cevin45x]

On the way back home, no noise at all... Wtf!?! Will see if it happens again tomorrow morning.

[mike the snake]

My diff makes a groan/growl/grumble when cold and when making the first tight turn or 2. After that it doesn't make any noise.

Maybe the torsen gears make noise when cold because the oil hasn't circulated? Once you make a turn and actually spin the internal gears which gets the oil back all over everything it quiets up.

This would be my guess.

[cevin45x]

Yeah but it bugs me that it never happened before, especially through last winter. And why isn't everyone experiencing the same thing? Mine isn't a growl, it's a scrapping sound.

Oh forgot to mention that it happened when I left my garage and when I got to work, 17 miles later on the hwy, it happened again at my work's parking lot.

[Ozzman]

Mine has done it since day one when first starting out of a parking space after sitting for a few hours or more. Feels kinda like clutch shudder but it isn't. I've felt similar in other LSD equipped vehicles.

[muffinz]

my car hasn't made an unusual "growling" or "shuddering" type noises/feels...

but every time I exit my driveway on cold tires, the outside rear wheel skips on the pavement and screeches when the car is unbalanced from the aprin vs street angle.

probably pisses my neighbors off.

[Suberman]

Originally Posted by rice_classic

Everything else you said is right but that because it's opinion. As long as the inside tire is connected to the ground and has traction the Torsen Diff will bias torque. That is the definition of limiting slip and quite succinctly so. It seems to me that your definition is that of a "locker" or a "locking differential". I know I'm being pedantic but I just want to clarify the semantics. (and now I'm rhyming...)

The Torsen Diff does meet the definition of a slip-limiting device.

There are even torsen diff's (like the WaveTrac) that utilize an internal arc ramp so that the diff functions even when the inside wheel becomes unloaded, which is something would have been nice on this car.

Not quite correct. If you lift one wheel off the ground a proper LSD will still allow torque to drive the car forward. An electronic brake LSD will also. A Torsen will not. Technically the slipping wheel actually has to slip for torque transfer to occur. A Torsen is not a locking LSD but the other types will all lock up. A Torsen only seems to lock up. To make it lock up requires an additional component as you say, which pretty much defeats the purpose of the Torsen and certainly isn't part of the original Torsen patent.

Fundamentally, a Torsen doesn't limit slip, it truly transfers torque. The torque transferred is proportional to the slip rate, the opposite of an LSD.

The design is fundamentally different. Torsen uses the slipping wheel to actually transfer torque to the wheel with traction. A true LSD brakes the slipping wheel against either the other wheel or the brake. No torque transfer occurs with a true LSD. In fact torque energy (hp) is absorbed and wasted. Very little hp is wasted driving a Torsen, one of its many advantages.

[rice_classic]

Originally Posted by Suberman

Fundamentally, a Torsen doesn't limit slip, it truly transfers torque. The torque transferred is proportional to the slip rate, the opposite of an LSD.

The Torque transfer is proportional to the ramp angle of the helical gears and associated friction surface, the total tractive force of the slipping tire and the slip rate.

Originally Posted by Suberman

Fundamentally, a Torsen doesn't limit slip, it truly transfers torque.

But that's the definition of a limited slip differential. It just does it differently (torque sensing) as opposed to something like a statically coupled clutch pack (speed sensing and/or torque sensing).

Your descriptions of how they work are appreciated . I'm not really hung up on the function of the units so much as I am on the subjective nature of the phrase; "not a true LSD".

I get what you're saying but this really is a "Rose by any other name" type of situation.



Clarification on WaveTrac goodness.

The additional component I speak of just allows it to continue to "limit slip" (AKA: transfer torque) even if the inside tire is unloaded (airborne). That is all.
http://wavetrac.net/technical.htm

It really does solve the 1 shortcoming of the Helical Gear LSD (the airborne tire).

Fun videos are fun:
[ame="http://www.youtube.com/watch?v=WluaaGy0HwA"]Wavetrac - YouTube[/ame]

[Suberman]

Originally Posted by rice_classic

The Torque transfer is proportional to the ramp angle of the helical gears and associated friction surface, the total tractive force of the slipping tire and the slip rate.

But that's the definition of a limited slip differential. It just does it differently (torque sensing) as opposed to something like a statically coupled clutch pack (speed sensing and/or torque sensing).

Your descriptions of how they work are appreciated . I'm not really hung up on the function of the units so much as I am on the subjective nature of the phrase; "not a true LSD".

I get what you're saying but this really is a "Rose by any other name" type of situation.



Clarification on WaveTrac goodness.

The additional component I speak of just allows it to continue to "limit slip" (AKA: transfer torque) even if the inside tire is unloaded (airborne). That is all.
http://wavetrac.net/technical.htm

It really does solve the 1 shortcoming of the Helical Gear LSD (the airborne tire).

Fun videos are fun:

OK, if you say so, but no automotive engineer regards a Torsen as an LSD. It is a true torque transfer, not a slip limiting device. The Torsen itself speeds up the slower axle, exactly opposite to a LSD, the engine need not add any more torque to effect this transfer. Torsen operate completely differently from LSD.

To get this effect with a LSD you need to do something technically elaborate like Audi does. Audi has a LSD that also speeds up the slower axle but it works differently from a Torsen.

Otherwise, a LSD does not transfer torque. The slipping axle is braked so as to allow engine torque to drive the slower axle. With a LSD the none jus driver more torque to speed up the slower axle. A Torsen continues to divide the torque as for an open diff but transfers unusable torque from the slipping axle to the axle with grip.

It is essential to understand this difference to understand how the Torsen works.

[rice_classic]

Originally Posted by Suberman

OK, if you say so, but no automotive engineer regards a Torsen as an LSD.

So it is semantics.


Cheers.

[Suberman]

Originally Posted by rice_classic

So it is semantics.


Cheers.

If you wish. But I encourage you to rethink this.

Until I viewed that goofy video and gave this whole issue a good think I couldn't figure out how the Torsen actually worked.

There is a fundamental difference and understanding that difference helps one understand how the Torsen works. It is very clever and quite different from other LSD solutions.

The key is to realize that the Torsen never limits slip. It actually divides the torque unequally across the differential gears as they are non reversing worm gears ( helical if you prefer but actually they have to be worm helixes).

Other LSD (except Audis trick axles) absorb engine torque going to the slipping wheel, sometimes 100% (which is half the available torque) which gets burned up, literally, in differential oil heat or brake pad wear. The Torsen doesn't do this. It merely transfers (biases) the unusable torque over to the wheel that can use it. This is a very important difference leading Subaru to fit this type of diff instead of a conventional LSD.

Engines with more power tend to have LSD rather than Torsen though there's no practical torque limit for a Torsen. They were fitted to US military spec HUMV.

[rice_classic]

From WIKI:

A limited-slip differential (LSD) is a type of automotive [ame="http://en.wikipedia.org/wiki/Differential_%28mechanics%29"]Differential (mechanical device) - Wikipedia, the free encyclopedia[/ame] gear arrangement that allows for some difference in angular [ame="http://en.wikipedia.org/wiki/Velocity"]Velocity - Wikipedia, the free encyclopedia[/ame] of the output shafts, but imposes a mechanical bound on the disparity.

Torsen/ATB Diffs meet the definition.

Originally Posted by Suberman

If you wish. But I encourage you to rethink this.

C'mon... you have got to see how stupid this is? People who say Torsens are not LSD's are only saying so as a reflection of their preference in design function. It's subjective, it's preference and that's all... It's like arguing about what a "real sports car" is and going 10 pages deep on the minutia of subjective opinions.

Until I viewed that goofy video and gave this whole issue a good think I couldn't figure out how the Torsen actually worked.

There is a fundamental difference and understanding that difference helps one understand how the Torsen works. It is very clever and quite different from other LSD solutions.

But the fact that it functions quite differently doesn't make it a "not-true-LSD". It just makes it a different type of LSD, but an LSD nonetheless. Also the Viscous Diff functions in a similar manner by biasing torque based on the slipping of the inside tire.

The key is to realize that the Torsen never limits slip. It actually divides the torque unequally across the differential gears as they are non reversing worm gears ( helical if you prefer but actually they have to be worm helixes).

Sorry but you keep saying this and it's not quite accurate nor does it validate your preference in terminology. We are talking slipping of tires, not slipping of the differential. We know that under cornering and with enough power an open diff will spin the inside tire, all rotational force going there (one tire fire), but the torque biasing of the Torsen, with the binding of the helical worm gears, will cease or limit that slipping tire. It meets the definition. All of this is assuming, of course, that the inside tire is touching the ground and has some tractive force.

Other LSD (except Audis trick axles) absorb engine torque going to the slipping wheel, sometimes 100% (which is half the available torque) which gets burned up, literally, in differential oil heat or brake pad wear. The Torsen doesn't do this. It merely transfers (biases) the unusable torque over to the wheel that can use it. This is a very important difference leading Subaru to fit this type of diff instead of a conventional LSD.

There's more reasons than that: Cost, serviceability, drive-ability, longevicty.. etc. Clutches and VC style diffs cost more or chatter at low speeds, less difficult for ABS system or need special fluids or wear out becoming open diffs as they age, etc.

Engines with more power tend to have LSD rather than Torsen though there's no practical torque limit for a Torsen. They were fitted to US military spec HUMV.

The Lexus LFA has a Torsen, STI's use Torsens, IS-F is torsen (2010+) and those are high-HP vehicles. I just can't believe that Toyota would put a "not-real-LSD" in a $300k sports car like the LFA.

Replies are in blue.

I'm sorry Suberman, I'm enjoying the back and forth but it really is subjective terminology and nothing else.

If you want to keep calling it a not-true-LSD I won't bug you anymore about it. You've been kind so I'll leave it alone.

[Suberman]

Your third point illustrates my point.

A true LSD limits slip when the spinning wheel has zero traction. The Torsen will not. This is a fundamental design difference.

What you choose to call it isn't important but understanding the difference is.

The torque biasing operation also makes the Torsen equipped car drive differently.

I've read journalists complain about the "soft" feel of the Torsen in the Nissan 370Z just for example. This comment illustrates the ignorance of said journalists. It is precisely because the Torsen does not limit wheel slip that it feels soft when it operates. By soft I think they mean progressive, which is the Torsen's singular advantage over other types.

[emutcfut]

Originally Posted by Suberman

I've read journalists complain about the "soft" feel of the Torsen in the Nissan 370Z just for example.

Pretty sure they came with a viscous LSD.