Does it INCREASE 'slipperyness' ..to stop clutch chatter......or does it DECREASE 'slipperyness'...to make the clutch plates grip better?
Does anyone actually know??
Does anyone actually know??
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What does a LS additive do?
- Thread starter code5coupe
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So, does it increase friction or decrease friction??
Hard to imagine it does both.
Does anyone know?
Hard to imagine it does both.
Does anyone know?
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MolaKule
Staff member
Chatter in Limited-Slip differentials with various clutch designs is a "Stick-Slip" phenomenon.
LSD Friction Modifiers in gear lubes do NOT refer to friction reduction.
Here, an LSD Friction Modifier refers to a chemical compound that gives rise to a situation such that the coefficient of friction (COF) varies Dynamically with respect to the relative speed of parts during engagement and disengagement in order to reduce or to eliminate chatter.
LSD Friction Modifiers in gear lubes do NOT refer to friction reduction.
Here, an LSD Friction Modifier refers to a chemical compound that gives rise to a situation such that the coefficient of friction (COF) varies Dynamically with respect to the relative speed of parts during engagement and disengagement in order to reduce or to eliminate chatter.
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But the clutch plates in a LSD are always engaged, there is no DISengagement. Even though they may slip (given enough torque), the pressure holding the plates in engagement is constant.
So, how does this compound know when the plates are slipping and when they are not and, more importantly, does it get more slippery when this happens (to reduce chatter) or does it get less slippery to lock up the plates (to reduce chatter)??
So, how does this compound know when the plates are slipping and when they are not and, more importantly, does it get more slippery when this happens (to reduce chatter) or does it get less slippery to lock up the plates (to reduce chatter)??
MolaKule
Staff member
Whether it is a synchronizer assembly in a Manual Transmission, a wet clutch AT transmission clutch pack, or a spring-loaded LSD clutch, the same operation applies.
That operation is one of the shearing of the chemical compound at the mating surfaces.
Various chemical compounds shear at various rates and depends mainly on three items;
1) applied pressure,
2) relative sliding or rotating speed,
3) surface texture and type.
SO, it is the shearing properties of the chemical compound at the surfaces of the clutch(s) that give rise to the Dynamic Coefficient of Friction.(DCF)
In the case of an LSD system specifically, the DCF of the friction-modifier compound at the mating surfaces reduces or eliminates a Stick-Slip situation.
That operation is one of the shearing of the chemical compound at the mating surfaces.
Various chemical compounds shear at various rates and depends mainly on three items;
1) applied pressure,
2) relative sliding or rotating speed,
3) surface texture and type.
SO, it is the shearing properties of the chemical compound at the surfaces of the clutch(s) that give rise to the Dynamic Coefficient of Friction.(DCF)
In the case of an LSD system specifically, the DCF of the friction-modifier compound at the mating surfaces reduces or eliminates a Stick-Slip situation.
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Does that friction compound work by increasing friction or by decreasing friction?
That is the question.
That is the question.
MolaKule
Staff member
Originally Posted by code5coupe
Does that friction compound work by increasing friction or by decreasing friction?
That is the question.
My explanations above should have led you to the conclusion that the answer to your question is, NO.
And I think I see the basis of your misunderstanding.
Many people see the phrase, "Friction Modification" and think friction reduction only. That is not correct.
Friction Modification can refer to three things, depending on the type of friction modifier compound and the application:
1) friction increase as in traction coefficient in CVT fluids to avoid chain/belt slippage,
2) friction reduction as in engine oils to increase fuel mileage,
3) dynamic friction as in a rotating or sliding mechanical assembly to accommodate different relative rotating or sliding speeds.
Does that friction compound work by increasing friction or by decreasing friction?
That is the question.
My explanations above should have led you to the conclusion that the answer to your question is, NO.
And I think I see the basis of your misunderstanding.
Many people see the phrase, "Friction Modification" and think friction reduction only. That is not correct.
Friction Modification can refer to three things, depending on the type of friction modifier compound and the application:
1) friction increase as in traction coefficient in CVT fluids to avoid chain/belt slippage,
2) friction reduction as in engine oils to increase fuel mileage,
3) dynamic friction as in a rotating or sliding mechanical assembly to accommodate different relative rotating or sliding speeds.
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MolaKule
Staff member
I reposted this in the Technical Discussion forum:
Remember, a Friction Modifier (FM) can be a friction reducer, a friction increaser, or one that controls friction in a specified manner.
In an engine, we want to reduce kinetic friction to increase fuel mileage.
In a CVT type AT we want a friction increaser so the chain/belt/pulley system can "get a grip."
In an Automatic Transmission or Limited Slip (LS) Differential, we want a controlled and specific type of friction.
The frictional characteristics we are discussing here is called Kinetic Friction, Dynamic Friction or Sliding Friction, a special kind of friction. Dynamic friction is a friction that changes its "coefficient of friction" as two surfaces that are in relative motion come into or are in contact as in an AT or in LS differential clutch plates.
Recall that AT clutch plates have alternating layers of clutch friction material and steel plates. The friction material is splined on the inside, where it locks to one of the gears. The steel plate is splined on the outside, where it locks to the clutch housing.
The pressure for the clutches is fed through passageways in the shafts. The hydraulic system controls which clutches are energized at any given moment.
In AT's and LS Differentials, we want the fluid to create a specific dynamic friction coefficient (dependent upon the clutch materials used) such that we have smooth engagement and disengagement, so we don't have shudder or slippage. Shudder and slippage cause increased frictional material wear and increased heat.
It is this complex package of frictional modifier chemical compounds found in ATFs and LS additives that is important for smooth operation.
Again, in an engine, we primarily want friction reduction. In an AT or LS Differential, we want controlled friction modification called Mu(V) in the literature.
Mu is the Coefficient of Friction and V is the relative velocity of rotating or sliding machine elements. In special friction test machines, the resulting curve of Mu(V) gives us the resulting Dynamic Friction Coefficient and it tells us how the friction coefficient value varies with the relative speeds of components.
The fluid chemistry must assist in providing a specific friction versus velocity relationship for the AT or LS Differential.
There is a phenomenon commonly called "stick-slip" or "dynamic frictional vibration" and manifests itself as "shudder" or low speed vibration in the vehicle. Using friction modifiers in the ATF or differential fluids prevents this shudder.
Remember, a Friction Modifier (FM) can be a friction reducer, a friction increaser, or one that controls friction in a specified manner.
In an engine, we want to reduce kinetic friction to increase fuel mileage.
In a CVT type AT we want a friction increaser so the chain/belt/pulley system can "get a grip."
In an Automatic Transmission or Limited Slip (LS) Differential, we want a controlled and specific type of friction.
The frictional characteristics we are discussing here is called Kinetic Friction, Dynamic Friction or Sliding Friction, a special kind of friction. Dynamic friction is a friction that changes its "coefficient of friction" as two surfaces that are in relative motion come into or are in contact as in an AT or in LS differential clutch plates.
Recall that AT clutch plates have alternating layers of clutch friction material and steel plates. The friction material is splined on the inside, where it locks to one of the gears. The steel plate is splined on the outside, where it locks to the clutch housing.
The pressure for the clutches is fed through passageways in the shafts. The hydraulic system controls which clutches are energized at any given moment.
In AT's and LS Differentials, we want the fluid to create a specific dynamic friction coefficient (dependent upon the clutch materials used) such that we have smooth engagement and disengagement, so we don't have shudder or slippage. Shudder and slippage cause increased frictional material wear and increased heat.
It is this complex package of frictional modifier chemical compounds found in ATFs and LS additives that is important for smooth operation.
Again, in an engine, we primarily want friction reduction. In an AT or LS Differential, we want controlled friction modification called Mu(V) in the literature.
Mu is the Coefficient of Friction and V is the relative velocity of rotating or sliding machine elements. In special friction test machines, the resulting curve of Mu(V) gives us the resulting Dynamic Friction Coefficient and it tells us how the friction coefficient value varies with the relative speeds of components.
The fluid chemistry must assist in providing a specific friction versus velocity relationship for the AT or LS Differential.
There is a phenomenon commonly called "stick-slip" or "dynamic frictional vibration" and manifests itself as "shudder" or low speed vibration in the vehicle. Using friction modifiers in the ATF or differential fluids prevents this shudder.
You try to separate two pages with dry fingers. It just don't work right.
Now you wet your fingers, then try again.
Works with no slip or shudder!
You used a friction modifier!
Now you wet your fingers, then try again.
Works with no slip or shudder!
You used a friction modifier!
Originally Posted by ford46guy
You try to separate two pages with dry fingers. It just don't work right.
Now you wet your fingers, then try again.
Works with no slip or shudder!
You used a friction modifier!
Kudos! Sometimes a simple nontechnical description is the best.
You try to separate two pages with dry fingers. It just don't work right.
Now you wet your fingers, then try again.
Works with no slip or shudder!
You used a friction modifier!
Kudos! Sometimes a simple nontechnical description is the best.
MolaKule
Staff member
Originally Posted by user52165
Originally Posted by ford46guy
You try to separate two pages with dry fingers. It just don't work right.
Now you wet your fingers, then try again.
Works with no slip or shudder!
You used a friction modifier!
Kudos! Sometimes a simple nontechnical description is the best.
But you weren't the OP asking the question about the FM's in a specific fluid, the FM in an LS differential.
After at least 5 simpler explanations were given by various members, the OP kept asking the same question.
This would lead one to believe that the OP either had a misunderstanding of friction or lacked some critical info about friction or both.
But that is ok since we are here to help provide technical (tribology) information for those who either have misunderstandings or lack some critical piece of information or both.
Originally Posted by ford46guy
You try to separate two pages with dry fingers. It just don't work right.
Now you wet your fingers, then try again.
Works with no slip or shudder!
You used a friction modifier!
Kudos! Sometimes a simple nontechnical description is the best.
But you weren't the OP asking the question about the FM's in a specific fluid, the FM in an LS differential.
After at least 5 simpler explanations were given by various members, the OP kept asking the same question.
This would lead one to believe that the OP either had a misunderstanding of friction or lacked some critical info about friction or both.
But that is ok since we are here to help provide technical (tribology) information for those who either have misunderstandings or lack some critical piece of information or both.
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The OP kept asking the same (simple) question because no ever answered it. (Still haven't.)
Some answers try to dazzle with technical terms that mean nothing to the layman, but didn't address the original question.
The OP still doesn't know what the effect friction modifier has on gear lube, i.e. does it increase or decrease friction?
Some answers try to dazzle with technical terms that mean nothing to the layman, but didn't address the original question.
The OP still doesn't know what the effect friction modifier has on gear lube, i.e. does it increase or decrease friction?
MolaKule
Staff member
Originally Posted by code5coupe
The OP kept asking the same (simple) question because no ever answered it. (Still haven't.)
Some answers try to dazzle with technical terms that mean nothing to the layman, but didn't address the original question.
The OP still doesn't know what the effect friction modifier has on gear lube, i.e. does it increase or decrease friction?
The OP's question has been answered in multiple ways and the OP should re-read the background information on Friction.
Here is another 'basic' explanation: The FM chemical compound modifies (changes) the Coefficient of Friction (COF) between the respective surfaces "on-the-fly" depending on the relative speeds of the rotating components and the applied pressure forces. That is, it decreases OR increases friction depending on the relative speeds of the rotating components and the applied pressure forces in order to prevent Stick-Slip which causes shudder.
The OP kept asking the same (simple) question because no ever answered it. (Still haven't.)
Some answers try to dazzle with technical terms that mean nothing to the layman, but didn't address the original question.
The OP still doesn't know what the effect friction modifier has on gear lube, i.e. does it increase or decrease friction?
The OP's question has been answered in multiple ways and the OP should re-read the background information on Friction.
Here is another 'basic' explanation: The FM chemical compound modifies (changes) the Coefficient of Friction (COF) between the respective surfaces "on-the-fly" depending on the relative speeds of the rotating components and the applied pressure forces. That is, it decreases OR increases friction depending on the relative speeds of the rotating components and the applied pressure forces in order to prevent Stick-Slip which causes shudder.
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Originally Posted by MolaKule
The OP's question has been answered in multiple ways and the OP should re-read the background information on Friction.
What background information are you referring to?
Something in this thread?
Originally Posted by MolaKule
Here is another 'basic' explanation: The FM chemical compound modifies (changes) the Coefficient of Friction (COF) between the respective surfaces "on-the-fly" depending on the relative speeds of the rotating components and the applied pressure forces. That is, it decreases OR increases friction depending on the relative speeds of the rotating components and the applied pressure forces in order to prevent Stick-Slip which causes shudder.
Sounds like some truly magical stuff if it can perform two opposing functions. Do you know what chemicals/elements are in this elixir? What does it do when there is no clutch involved, as in an open diff? Does it increase or decrease friction or does it do nothing at all in an open diff? What about when it's used in a helical gear-type limited slip, does it know when to slip and when to not slip in that situation?
The OP's question has been answered in multiple ways and the OP should re-read the background information on Friction.
What background information are you referring to?
Something in this thread?
Originally Posted by MolaKule
Here is another 'basic' explanation: The FM chemical compound modifies (changes) the Coefficient of Friction (COF) between the respective surfaces "on-the-fly" depending on the relative speeds of the rotating components and the applied pressure forces. That is, it decreases OR increases friction depending on the relative speeds of the rotating components and the applied pressure forces in order to prevent Stick-Slip which causes shudder.
Sounds like some truly magical stuff if it can perform two opposing functions. Do you know what chemicals/elements are in this elixir? What does it do when there is no clutch involved, as in an open diff? Does it increase or decrease friction or does it do nothing at all in an open diff? What about when it's used in a helical gear-type limited slip, does it know when to slip and when to not slip in that situation?
Originally Posted by ford46guy
You try to separate two pages with dry fingers. It just don't work right.
Now you wet your fingers, then try again.
Works with no slip or shudder!
You used a friction modifier!
The friction modifier you mentioned here increases friction.
Is that what the friction modifier in my LS diff does??
That's been my question all along, can you answer it?
You try to separate two pages with dry fingers. It just don't work right.
Now you wet your fingers, then try again.
Works with no slip or shudder!
You used a friction modifier!
The friction modifier you mentioned here increases friction.
Is that what the friction modifier in my LS diff does??
That's been my question all along, can you answer it?
MolaKule
Staff member
Originally Posted by code5coupe
Originally Posted by MolaKule
The OP's question has been answered in multiple ways and the OP should re-read the background information on Friction.
What background information are you referring to?
Something in this thread?
Yes, obviously Posts 5151172, 5153004, 5153027, 5153191, and 5157818 are being referred to and I suggest you review and study them.
Originally Posted by MolaKule
Here is another 'basic' explanation: The FM chemical compound modifies (changes) the Coefficient of Friction (COF) between the respective surfaces "on-the-fly" depending on the relative speeds of the rotating components and the applied pressure forces. That is, it decreases OR increases friction depending on the relative speeds of the rotating components and the applied pressure forces in order to prevent Stick-Slip which causes shudder.
Originally Posted by code5coupe
Sounds like some truly magical stuff if it can perform two opposing functions. Do you know what chemicals/elements are in this elixir?
There are no opposing functions involved here, which continues to show your misunderstanding of the subject. For the third time, the FM chemistry modifies the COF on the fly according to relative speeds and applied pressures.
Do I know what chemistry is used in LS additives? Of course.
Originally Posted by code5coupe
What does it do when there is no clutch involved, as in an open diff? Does it increase or decrease friction or does it do nothing at all in an open diff? What about when it's used in a helical gear-type limited slip, does it know when to slip and when to not slip in that situation?
Had you studied Posts 5151172, 5153004, 5153027, 5153191 and 5157818 you will see I have never stated this LS additive applies to Torque sensing Torsen-type differentials.
That is a different topic entirely.
Had you googled this
"The Torsen differential* is a purely mechanical device; it has no electronics, clutches or viscous fluids. The Torsen (from Torque Sensing) works as an open differential when the amount of torque going to each wheel is equal. ... The design of the gears in the differential determines the torque bias ratio.
"
https://auto.howstuffworks.com/differential6.htm
you could have answered your own question.
Originally Posted by MolaKule
The OP's question has been answered in multiple ways and the OP should re-read the background information on Friction.
What background information are you referring to?
Something in this thread?
Yes, obviously Posts 5151172, 5153004, 5153027, 5153191, and 5157818 are being referred to and I suggest you review and study them.
Originally Posted by MolaKule
Here is another 'basic' explanation: The FM chemical compound modifies (changes) the Coefficient of Friction (COF) between the respective surfaces "on-the-fly" depending on the relative speeds of the rotating components and the applied pressure forces. That is, it decreases OR increases friction depending on the relative speeds of the rotating components and the applied pressure forces in order to prevent Stick-Slip which causes shudder.
Originally Posted by code5coupe
Sounds like some truly magical stuff if it can perform two opposing functions. Do you know what chemicals/elements are in this elixir?
There are no opposing functions involved here, which continues to show your misunderstanding of the subject. For the third time, the FM chemistry modifies the COF on the fly according to relative speeds and applied pressures.
Do I know what chemistry is used in LS additives? Of course.
Originally Posted by code5coupe
What does it do when there is no clutch involved, as in an open diff? Does it increase or decrease friction or does it do nothing at all in an open diff? What about when it's used in a helical gear-type limited slip, does it know when to slip and when to not slip in that situation?
Had you studied Posts 5151172, 5153004, 5153027, 5153191 and 5157818 you will see I have never stated this LS additive applies to Torque sensing Torsen-type differentials.
That is a different topic entirely.
Had you googled this
"The Torsen differential* is a purely mechanical device; it has no electronics, clutches or viscous fluids. The Torsen (from Torque Sensing) works as an open differential when the amount of torque going to each wheel is equal. ... The design of the gears in the differential determines the torque bias ratio.
"
https://auto.howstuffworks.com/differential6.htm
you could have answered your own question.
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