Torque Converter Friction

1. Torque Converter Friction ITALL BEGINS WITH A KISS Presented by: Frank Slocum VP, Marketing & Sales Raybestos Powertrain, LLC

2. 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.

3. 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.

4. Torque Converter Friction • Imagination • Get inside of your Converter • Creative License to Describe “What is Happening” • The World According toFrank

5. 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.

6. 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.

7. 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.

8. Torque Converter Friction • Still millions and millions of oil molecules are slicing across the friction face. • Relative torque is rising as the piston’s 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.

9. 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.

10. Torque Converter Friction Let’s 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.

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

12. Torque Converter Friction Ever see a puddle with a single drop of oil flashing the rainbow of colors?

13. 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 .

14. Torque Converter Friction Let’s 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.

15. 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.

16. 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.

17. 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.

18. 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.

19. 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.

20. 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.

21. 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.

22. 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.

23. 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.

24. Torque Converter Friction • Phew, we got through that didn’t we. • I will now ask your imaginative indulgence again…

25. 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.

26. Torque Converter Friction • If there were enough, you couldn’t 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.

27. 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 1:1. • The term used is “Friction coefficient” and dynamic is usually between 0.10 to 0.14 • Static is between 0.08 and 0.16

28. Torque Converter Friction From a “Goodness” or smooth operating point of view: • The closer the ratios are to each other and 1:1 the better. • When static is higher than dynamic, we could see “Stick-slip” or chatter.

29. 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

30. 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.

31. Torque Converter Friction Let’s talk about two aspects that we look for in friction materials: • Compliance • Resilience

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

33. 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.

34. 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.

35. Torque Converter Friction Ever heard “ You can’t get a steel plate too smooth.”? • I’d like for a reaction surface to be Ra 8 or better with no scratches. • I’d like flatness to be 0.003 or better in the friction and reaction surface. • Both are very hard to do.

36. 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.

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

38. 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 .

39. 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

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

41. 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.

42. 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.

43. Torque Converter Friction Let’s talk about resilience for a few minutes. • Can we define it as the ability to return to its original form? • A resistance to change.

44. 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.

45. 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.

46. 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, can’t hold the fibers together.

47. 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.

48. 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 .

49. 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 doesn’t generate heat at the oil interface.

50. 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.