Torque Converter Friction

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Torque Converter Friction

• IT ALL BEGINS WITH A KISS

Presented by Frank Slocum VP, Marketing
Sales Raybestos Powertrain, LLC
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Torque Converter Friction

• We are going to discuss today six subjects areas
• What happens in that transitional phase of piston
  travel from 0.001 to 0.000. I call it the
  Kiss Phase.
• We are going to discuss how lock-up works.

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Torque Converter Friction

• How the different friction materials do their
  jobs.
• How the different fluids behave.
• 5. Intermixed with continuous slip and the other
  factors.
• 6. Finally, we will cover some assembly
  considerations, along with surface finishes.

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Torque Converter Friction

• Imagination
• Get inside of your Converter
• Creative License to Describe
• What is Happening
• The World According to Frank

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Torque Converter Friction

• Imagine you are inside of your torque converter
• The solenoid closed, the TC valve has
• shuttled, flow has reversed, and charge pressure
  is building on the backside of the piston, moving
  it forward, closer and closer to the to the
  carefully machined cover.

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Torque Converter Friction

• A whole lot is going on as the fluid, under 60psi
  charge pressure, is trying to squeeze around the
  edge of the piston, across the face of the
  friction, trying to go to low pressure.
• The cover, attached to the engine, is rotating
  faster than the piston, which is mounted on the
  driven turbine.

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Torque Converter Friction

• The oil, which was once appearing very fluid and
  slippery, is now starting to create drag as the
  friction material nears the cover.
• The relative speed between the piston and cover
  begin to slow.
• Right now the thickness of your note paper
• is fat compared to the oil film thickness.

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Torque Converter Friction

• Still millions and millions of oil molecules are
  slicing across the friction face.
• Relative torque is rising as the pistons
  relative speed slows, and
• the torsional springs begin to compress as the
  individual cylinders fire.
• The stator is now freewheeling as the converter
  enters the coupled mode.

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Torque Converter Friction

• Torque is now being transmitted by the converter
  as a coupling, and by the rising torque of
  molecular oil drag across the friction face
• We are now entering into the KISS Phase - the
  point where everything changes, and the
  uniqueness of an oil film comes into play.

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Torque Converter Friction

• Lets take mental shift here and ask the
  question, How thick is an oil film?
• A thousandth of an inch?
• A half thousandth?
• A hundredth of a thousandth
• And so on.

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Torque Converter Friction

• Actually, an oil film is one molecule thick.
• Let me put that in perspective.

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Torque Converter Friction

• Ever see a puddle with a single drop of oil
  flashing the rainbow of colors?

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Torque Converter Friction

• That is an oil film one molecule thick.
• And when it gets to that thickness it behaves
  entirely different than you can even imagine.
• It behaves like a solid.
• And its thickness is measured in angstroms,
  inches to the umteen decimals .

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Torque Converter Friction

• Lets go back into imagination again.
• The piston continues to move closer and closer,
  and there is relative movement between the cover
  and friction material.
• We are now less than a quarter of a thousandth of
  an inch, and the oil is squirting like a knifedge
  all around the interface, going every which way.

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Torque Converter Friction

• A little more imagination here
• Think of oil molecules being like spaghetti right
  out of the boiling water, and millions of them
  are in every droplet.

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Torque Converter Friction

• Slipping and sliding one over the other,
  unanchored, moving about trying to get someplace
  another molecule is not.
• Rubbing, one against the other.

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Torque Converter Friction

• And that rubbing causes friction, one on another,
  and in this highly excited state, the temperature
  starts to rapidly rise.
• Up, and up, goes the temperature, and the
  unrelenting apply force continues to close the
  interface between friction and cover.
• Individual oil molecules see hundreds of degrees
  of temperature rise that dissipate
• as the oil reaches the backside of the piston.

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Torque Converter Friction

• The combined interface is now seeing temperatures
  in the hundreds of degrees
• with the unrelenting, violent, slicing oil film,
  accelerating across the interface.
• Half again, and half again, the interface closes.

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Torque Converter Friction

• The spaghetti molecules squirm to escape the
  ever closer friction and steel.
• When suddenly a dramatic change begins to take
  place
• The beginning of an exponential rise in torque
  begins, two becomes four, four becomes sixteen,
  then 256, 65536, and on.

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Torque Converter Friction

• As individual oil molecules stand up and resist
  the relative movement, individually resisting and
  then releasing as they loose grip, their
  directional orientation has changed and instead
  of squirting away, they are standing and
  resisting.
• We are now in the KISS phase.

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Torque Converter Friction

• Here, the interface is approaching the one
  molecule thickness between the parts.
• Most would say they are in contact, but they are
  not, and in fact the molecules themselves are
  drawing the interfaces together, as if in an
  embrace.

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Torque Converter Friction

• We are now moving from the Hydrodynamic phase
  into the boundary level lubrication where the oil
  film is reduced to a minimum.
• The additives are now shearing as they realign.

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Torque Converter Friction

• We are now in lock-up.
• Interface temperatures go down as the heat
  transfers into the steel.
• Limited oil quantity flows between the friction
  fibers from high charge pressure to low drain
  pressure.
• And the robust resistance to slippage is holding.

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Torque Converter Friction

• Phew, we got through that didnt we.
• I will now ask your imaginative indulgence again

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Torque Converter Friction

• Think of running your hand across a bristle
  brush.
• You feel the stiffness of each bristle as it
  holds and then suddenly releases.
• And resets its resistance.

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Torque Converter Friction

• If there were enough, you couldnt move your
  hand the only choice you have is to reduce
  pressure, allowing your hand to move.
• That is static friction and the friction during
  movement is dynamic friction.

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Torque Converter Friction

• There are two types of simple friction
• Dynamic or moving
• Static or holding
• They are expressed as a ratio, and usually near
  11.
• The term used is Friction coefficient and
  dynamic is usually between 0.10 to 0.14
• Static is between 0.08 and 0.16

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Torque Converter Friction

• From a Goodness or smooth operating point of
  view
• The closer the ratios are to each other and 11
  the better.
• When static is higher than dynamic, we could see
  Stick-slip or chatter.

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Torque Converter Friction

• The oil used and calibration are the keys.
• The computer controls calibration
• You control the oil
• Ford Mercron for Ford
• GM Dexron For GM
• Chrysler for Chrysler
• Honda for Honda

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Torque Converter Friction

• The standard Raybestos tan clutch is a good match
  for the standard OEM materials.
• Upgraded materials are a good choice for
  durability and life.

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Torque Converter Friction

• Lets talk about two aspects that we look for in
  friction materials
• Compliance
• Resilience

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Torque Converter Friction

• Compliance is the ability to comply with minor
  variations between the interacting surfaces in
  rotation.

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Torque Converter Friction

• Resilience is the ability to return to the
  original dimensions and shape after being
  compressed.
• A sponge is a simple example. Squeeze it it
  compresses, release and it resumes its original
  shape.

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Torque Converter Friction

• Our interface is three parts, the friction, the
  oil, and the steel.
• The steel surface is just as important as the
  friction.
• For maximum contact, the material must comply
  with small imperfections in the cover.

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Torque Converter Friction

• Ever heard You cant get a steel plate too
  smooth.?
• Id like for a reaction surface to be Ra 8 or
  better with no scratches.
• Id like flatness to be 0.003 or better in the
  friction and reaction surface.
• Both are very hard to do.

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Torque Converter Friction

• So if we are in the Kiss phase, and we have
  high compliance parts,
• And we have a very smooth reaction steel surface,
  we will maximize our torque capacity.
• We are going to get a very smooth transition to
  one-to-one.

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Torque Converter Friction

• Once we get to this point, we can look to extend
  engagement time or continuous slip.

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Torque Converter Friction

• When we continuously slip or extend the
  engagement time, we
• See a dramatic increase in interface temperature.
• See a requirement for higher strength materials .

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Torque Converter Friction

• Because we are Working the oil, we see a
  surface temperature of over 600 F.
• This can scorch and burn organic materials
• Scorch conventional resins
• Breakdown the oil and fill the oil channels with
  varnish
• Drive the dynamic torque down
• Dramatically lower static friction

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Torque Converter Friction

• Fact Static coefficient directly relates to
  temperature.
• Static friction falls in relation to higher
  temperature at almost a 1F to 1 basis.
• Therefore, it is advantageous to keep converter
  charge oil temperature under control.
• Charge oil is transmission sump oil.

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Torque Converter Friction

• Because of the scorching, we move away from
  traditional organic cellulose materials and move
  to more sophisticated fibers.
• Glass and aramid fibers, such as Kevlar
• are blended into the friction material.
• High temperature resins are used.
• Higher strength resins are used.

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Torque Converter Friction

• Generally, the dynamic friction goes down
• because the resilience goes down
• The friction ring is densified, made more
  compact, and the component materials are of lower
  friction.
• Tradeoffs are the way it is done.

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Torque Converter Friction

• Lets talk about resilience for a few minutes.
• Can we define it as the ability to return to its
  original form?
• A resistance to change.

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Torque Converter Friction

• Think of a regular coil spring, like an
  accumulator spring.
• You can cycle that spring millions of times in a
  certain range and have no ill effect.
• But if you go to far, over compress it,
  compact it to a solid, it will only last so long.

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Torque Converter Friction

• In a spring, it breaks into pieces.
• In a torque converter, the material develops
  cracks, they join together and pieces flake.
• The cause is excessive clamp force, aggravated by
  thermal stress.
• The solution is to upgrade the material
• or add more friction surfaces.

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Torque Converter Friction

• One other disintegration mode has to be addressed
  - Erosion.
• The hot compressed oil jets that exist at the
  interface will also erode or abrade the material.
• The cause is insufficient material strength, the
  resin, at temperature, cant hold the fibers
  together.

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Torque Converter Friction

• Unfortunately, this debris is very fine and
• flows through the cooler out line to become
  trapped in the heat exchanger.
• Which reduces flow, raises temperature in the
  converter and the vehicle is on its way to
  failure.

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Torque Converter Friction

• So how much heat does this interface develop?
• Enough to discolor a converter cover!!
• That is why we need carbon rings.
• The spun wound SW Carbon ring is 100
  carbon-carbon continuous fiber, held in position
  by resin and bond adhesive .

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Torque Converter Friction

• The friction is low for carbon fiber because it
  is slippery by nature, and because it is a very
  compacted wafer.
• It is not resilient, so the dynamic is low.
• It is temperature resistant and uses the cover as
  a big heat sink to carry off energy.
• But mostly, it doesnt generate heat at the oil
  interface.

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Torque Converter Friction

• A fun question for a moment
• If all the fibers in a single Raybestos
  Spun-Wound torque ring were laid end to end,
  into a single fiber, how long would it be?
• How many feet long?
• Guess and write it down.

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Torque Converter Friction

• Ready for the answer??

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Torque Converter Friction

• Ready for the answer??
• It is over 121,000 feet -- roughly 23 miles.

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Torque Converter Friction

• How much torque can an automotive lock- up system
  transmit?
• It is a good question that needs answering.

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Torque Converter Friction

• It is about 460 lb-ft of torque (298MM, 125 psi
  charge).
• Not a lot, is it?? And if we continue to force
  slip it, we will burn it out.
• Changing material to a higher static material
  increases holding torque capacity.
• To further increase capacity, we need to add
  friction surfaces, multiple clutches.

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Torque Converter Friction

• So where we see these diesel trucks with a
  multiple disc package, that is what they are
  trying to do, add capacity.
• But if you dont have the steel heat sink, the
  plates will warp, you will loose compliance and
  surface contact, static friction will go down,
  slip will increase,
• temperature goes up, converter fails.

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Torque Converter Friction

• So what can you do as rebuilders?
• Select your friction material carefully.
• Match your friction to the intended duty cycle.
• Exercise care when bonding, and insist on a
  contamination free surface.
• Tack check your adhesive to insure freshness.

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Torque Converter Friction

• Make sure the interface surface is smooth and
  flat.
• Consider the amount of piston movement and
  material thickness.
• Axially align your converter from pilot to hub.
• Tack, then finish weld.

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Torque Converter Friction

• When finished, put about ½ pint of transmission
  oil in the converter as a rust preventative and
  break in oil.
• Take pride in your good work.

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Torque converter Friction

• So lets review what we have covered
• We have seen the transitional phase.
• We have discussed lock up.
• We have touched on friction materials.
• We have discussed fluids.
• And reassembly considerations.

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Torque Converter Friction

• Now lets cover questions.
• What we cant answer, we will try to get the
  answer from our Tech Center.
• And remember, It all begins with a kiss

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Torque Converter Friction

• Thanks for spending your time with us.
• Enjoy Indianapolis.