Torsen vs standard Traction lok LSD differential pros and cons?

[WD Pro]

Does anybody have an illustration of exactly what our Ford Torsens look like? How many sets of worm gears it has: 3 or 4? It's not easy to visualize how a different fluid (or friction modifier) can alter TBR, but it does, because when you have excessive chatter, and you add FM, it stops, meaning it makes the differential less aggressive indeed.

Not exactly what you asked for, but this photo courtesy of @JohnVallo may help :

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[shogun32]

In other words, I want the diff to allow the wheels to rotate at different speeds, but only as long as both are rotating at least to some degree. The wheels should rotate either together (at different speeds if need be), or not at all.

I agree, that is the only config that makes any sense.

If the wheel that is freely spinning (ice or up in the air) had the brake applied so it stopped spinning freely (heavy drag, not fully stopped) would that accomplish the task?

 

[Norm Peterson]

A spool is no good for cornering, but great when one wheel has no grip.

No good for street driving, true (they'll chirp and chatter in at least the tighter corners). But they're not quite as bad on a race track where most corner radii are big multiples of the car's rear track width and you're unloading the inside rear tire as much as your need for corner exit acceleration can stand. IIRC, NASCAR actually lists spools as one of two legal options (the other being the Detroit locker, which doesn't like to take corners much better under power when it essentially becomes a spool).

A Torsen is good for cornering, but no good when one wheel has no grip at all.

So what would that indicate?

There may not be much you can do about the inside rear wheel momentarily "getting air" after rolling over an apex curbing at the track except running wider and staying off the curbings. But you can fix situations where you have either a little too much rear bar or not enough front roll stiffness. You'd end up with a bit more understeer, but there might be something you could do with toe link inclination to loosen things up a little without affecting rear load transfer.


Norm

 

[Vlad Soare]

If the wheel that is freely spinning (ice or up in the air) had the brake applied so it stopped spinning freely (heavy drag, not fully stopped) would that accomplish the task?

Yes, I think it would. Actually, I believe there are 4WD systems which do just that - use open differentials, then rely on the ESC to slow down the spinning wheel(s) to some degree.
But I'm not sure this can be achieved by purely mechanical means, just by the design of the diff itself. Or is it?

There may not be much you can do about the inside rear wheel momentarily "getting air" after rolling over an apex curbing at the track except running wider and staying off the curbings. But you can fix situations where you have either a little too much rear bar or not enough front roll stiffness. You'd end up with a bit more understeer, but there might be something you could do with toe link inclination to loosen things up a little without affecting rear load transfer.

Having one wheel in the air for a tiny amount of time is one thing, but I was thinking rather about trying to drive off from a standstill when one rear wheel is on ice. The Torsen will send 2.8 times the torque required to spin that wheel to the other wheel. But is it enough? I suspect it isn't.

 

[jwt]

Before stability control etc the proper way to regain traction if one wheel had no traction say on ice was to gently apply handbrake. The torque load on the spinning wheel caused by handbrake caused the tbr ratio torque to be applied to the wheel with grip. Made it up a hill many a time with that trick. No good for high speed situations but maybe traction control can do same by applying brake to inner wheel ?

 

[Vlad Soare]

Before stability control etc the proper way to regain traction if one wheel had no traction say on ice was to gently apply handbrake. The torque load on the spinning wheel caused by handbrake caused the tbr ratio torque to be applied to the wheel with grip.

Say, that's a neat idea!

 

[Norm Peterson]

Having one wheel in the air for a tiny amount of time is one thing, but I was thinking rather about trying to drive off from a standstill when one rear wheel is on ice. The Torsen will send 2.8 times the torque required to spin that wheel to the other wheel. But is it enough? I suspect it isn't.

Quick and dirty math says . . .

3950# x 0.46 = 1819# rear weight. Times mu = 0.05 (I'm thinking wet ice here and trying to under-estimate) gives ~90 lbs at one rear tire and ~250 lbs at the other, 340 lbs total. That's more than enough to get you rolling on level ground or mild slopes (less than, say, half of 340/3950, or 4% or so).


Norm

 

[Jaymar]

Before stability control etc the proper way to regain traction if one wheel had no traction say on ice was to gently apply handbrake. The torque load on the spinning wheel caused by handbrake caused the tbr ratio torque to be applied to the wheel with grip. Made it up a hill many a time with that trick. No good for high speed situations but maybe traction control can do same by applying brake to inner wheel ?

If I'm not mistaken that's basically what E-diffs do. Must have been designed by some guy that got his open diff stuck on a dirt road before cell phones when he was a kid.

 

[shogun32]

If I'm not mistaken that's basically what E-diffs do. Must have been designed by some guy that got his open diff stuck on a dirt road before cell phones when he was a kid.

Or designed a car without a handbrake - looking at you modern Camaro. Frickin' buttons!

 

[Jaymar]

Or designed a car without a handbrake - looking at you modern Camaro. Frickin' buttons!

Yeah, who does that? That should be an interview question, if you're willing to take the handbrake out of a fun car you shouldn't be designing fun cars because you clearly don't get it.

 

[Brian@BMVK]

A spool is no good for cornering, but great when one wheel has no grip. A Torsen is good for cornering, but no good when one wheel has no grip at all.
What I want is a combination of both. One that's ideal in both situations. One that allows you to drive round a corner smoothly, but never, under any circumstances, spins one wheel while the other is completely stationary. If one wheel spins while the other is stationary, then I want the other to receive as much torque as is necessary for it to move.
In other words, I want the diff to allow the wheels to rotate at different speeds, but only as long as both are rotating at least to some degree. The wheels should rotate either together (at different speeds if need be), or not at all.
Is this possible? I guess not. At least not by mechanical means. Not without some kind of electronic control, based on input from the ABS sensors, or something like that.

Wavetrac

 

[Norm Peterson]

Yeah, who does that? That should be an interview question, if you're willing to take the handbrake out of a fun car you shouldn't be designing fun cars because you clearly don't get it.

Chevy isn't the only guilty party - the P-brake was also electric on the 2010 Subaru Legacy 2.5GT. The LGT was the top-of-the-food-chain Legacy as far as sportiness was concerned (turbocharged with a manual 6-speed).

I hated having to use a button (with its zero modulation capability), and used it as little as possible. Liked the car otherwise.


Norm

 

[Vlad Soare]

Wavetrac

Thanks, Brian. I looked it up, and at first glance it seems to be just what I was talking about. As far as I can see, it seems to be a kind of Torsen basically, i.e. fully mechanical, no wear parts, etc., but with an extra mechanism that artificially puts some load on a wheel when it has none. That's really intriguing. I'd love to know how it manages that.

 

[Elp_jc]

Not without some kind of electronic control, based on input from the ABS sensors, or something like that.

That's exactly what 'Torque Vectoring' would do, so just get that, and problem solved. Ha ha. I don't think our cars have that. But all the hardware is already in place; it's simply a more sophisticated version of ESC (electronic stability control).

 

[Bahndvr]

Would a Wavetrac make for a cooler rear diff?

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