Dominant1
Well-Known Member
Yeah road courses reek havoc on rears, alot more constant pressure then a drag strip...
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EXP Jawa
Well-Known Member
- Joined
- Jun 9, 2014
- Threads
- 3
- Messages
- 1,011
- Reaction score
- 205
- Location
- Rochester, NY
- Website
- www.torsen.com
- First Name
- Rick
- Vehicle(s)
- 1999 Cobra Convertible, Electric Green
The term "limited slip" refers to a product that limits wheel slip. As some have said, it really is an over-arching, general term that includes several different product types. Anything that is not strictly open and not full-locking. So, yes, Torsen (and other helical gear diffs) are limited slip differentials. I promise you that if you contact Torsen tech support and ask if its a limited slip, that person will tell you "yes". That category also includes various forms of clutch plate diff, preloaded diffs (which can be applied to helical gear as well), viscous diffs, as well as electronic-controlled diffs. So, lets not get hung up on nomenclature.
Speaking of nomenclature, the OP used "Torsen" (as a name) and "torsen" (as a category). Capitalized or not, Torsen is still a trademark and a specific brand name. It is incorrect to use as a general term. Sort of like how Kleenex is still a trademarked brand name even if you're actually buying store-brand tissues. Or maybe more appropriately, how the term "Positraction" is still an Eaton trademark, even though people use it for any LSD. It shouldn't be. I digress.
I'm not sure why you'd claim that a True Trac is stronger than a Torsen. There may be applications where that's true and applications where its not. Both are the same type of product, and for any given application, would be designed to be whatever their designers thought the best compromise for the situation.
The patent on one step of the Torsen cross-axis design was patented in 1958, but if you think that is the only patent ever on the product type, you're quite mistaken. The best way to protect your technology is to keep moving it forward, continue to develop it and file for subsequent improvement patents. What Vern Gleasman patented in the '50s was an ancestor to the Torsen diffs that went into production in the '80s, and where markedly improved by Gleason Works. There are file cabinets full of Torsen patents. What's more is that the current model Torsen differentials across many applications don't use that crossed-axis design anymore and haven't for many years. There are several different Torsen product families. The designs used in the S197 & S550 applications are variations of the Type-2 & T-2R, which are parallel-axis.
Incidentally (and I've said this here before), the operating theory of the crossed-axis Torsen working by gears spinning one way and not the other is an old wives' tale. It doesn't work that way in reality. Helical gear diffs work because they generate friction internally on the gearing, rather than on a clutch. That friction scales with torque input, so it can differentiate easily at low speed/torque and lock hard at full throttle. That leads to progressive torque transfer behavior without dulling a car's turn-in response.
One other comment - typical (inexpensive) clutch plate diffs work by using the preload spring to put a constant load across the clutch plates. This generates a fairly fixed amount of friction. Increased torque on the side gears will generate some added friction by increasing gear thrusts on the clutches, but that's relatively minor. Because these diffs rely on friction to resist slip, they also rely on having a supporting reaction torque to operated, just like a helical gear diff does. You need to have some amount of traction under both tires to be fully operable. Unless a plate diff is extremely tight - such that it understeers like a pig - it will also allow a raised wheel to spin. It is quite true that the preloading does allow some torque to transfer to the grounded wheel under these conditions, but only in the amount of the break-away torque times the diff's torque bias ratio (for a Traction-Loc is about 1.8:1). That isn't a huge amount of torque, and certainly not enough to prevent wheel spin. One just hopes that the tire is raised off the ground for only a moment and the preload can carry you through. But that isn't as much of an advantage as people make it out to be, and has to be balanced against the understeer it adds and the loss of crisp steering response.
Just my $0.02...
Speaking of nomenclature, the OP used "Torsen" (as a name) and "torsen" (as a category). Capitalized or not, Torsen is still a trademark and a specific brand name. It is incorrect to use as a general term. Sort of like how Kleenex is still a trademarked brand name even if you're actually buying store-brand tissues. Or maybe more appropriately, how the term "Positraction" is still an Eaton trademark, even though people use it for any LSD. It shouldn't be. I digress.
I'm not sure why you'd claim that a True Trac is stronger than a Torsen. There may be applications where that's true and applications where its not. Both are the same type of product, and for any given application, would be designed to be whatever their designers thought the best compromise for the situation.
The patent on one step of the Torsen cross-axis design was patented in 1958, but if you think that is the only patent ever on the product type, you're quite mistaken. The best way to protect your technology is to keep moving it forward, continue to develop it and file for subsequent improvement patents. What Vern Gleasman patented in the '50s was an ancestor to the Torsen diffs that went into production in the '80s, and where markedly improved by Gleason Works. There are file cabinets full of Torsen patents. What's more is that the current model Torsen differentials across many applications don't use that crossed-axis design anymore and haven't for many years. There are several different Torsen product families. The designs used in the S197 & S550 applications are variations of the Type-2 & T-2R, which are parallel-axis.
Incidentally (and I've said this here before), the operating theory of the crossed-axis Torsen working by gears spinning one way and not the other is an old wives' tale. It doesn't work that way in reality. Helical gear diffs work because they generate friction internally on the gearing, rather than on a clutch. That friction scales with torque input, so it can differentiate easily at low speed/torque and lock hard at full throttle. That leads to progressive torque transfer behavior without dulling a car's turn-in response.
One other comment - typical (inexpensive) clutch plate diffs work by using the preload spring to put a constant load across the clutch plates. This generates a fairly fixed amount of friction. Increased torque on the side gears will generate some added friction by increasing gear thrusts on the clutches, but that's relatively minor. Because these diffs rely on friction to resist slip, they also rely on having a supporting reaction torque to operated, just like a helical gear diff does. You need to have some amount of traction under both tires to be fully operable. Unless a plate diff is extremely tight - such that it understeers like a pig - it will also allow a raised wheel to spin. It is quite true that the preloading does allow some torque to transfer to the grounded wheel under these conditions, but only in the amount of the break-away torque times the diff's torque bias ratio (for a Traction-Loc is about 1.8:1). That isn't a huge amount of torque, and certainly not enough to prevent wheel spin. One just hopes that the tire is raised off the ground for only a moment and the preload can carry you through. But that isn't as much of an advantage as people make it out to be, and has to be balanced against the understeer it adds and the loss of crisp steering response.
Just my $0.02...