davenew

For the nerds, and other interested parties. You might want to save this file to your hard drive.

This pdf file goes into very detailed description of various clutch types and history, including SAC pressure plate, etc. In case you're not familiar, the B5 S4 uses a dual mass flywheel and a pressure plate with self adjusting clutch (SAC) feature.

Here's a preview (dual mass flywheel info):

"The increase in noise sources owing to inadequate natural damping is a noticeable feature of modern automotive construction. The causes lie in the reduced weight of the vehicles and in the wind-tunnel optimised bodies, whose low wind noise now makes other noise sources perceptible. But also sleek body designs and extremely low-revving engines, as well as 5-speed transmissions and thin oils, contribute to this phenomenon. The periodical combustion process of the reciprocating engine induces torsional vibrations in the drive train, which as transmission rattle and body noise interfere with driving comfort.

Function:
Physical study of drive trains has revealed that the resonance speed range can be shifted by changing the allocation of angular moments. As the transmission angular momentum increases, the resonance speed, which generates loud noise, drops below the idle speed and thus falls outside the engine's rev range. Using the dual-mass flywheel (DMF), LuK was able to develop a large-scale product that embodies this principle and thereby keeps resonance amplitude extremely low.
As shown in the "function" diagram, with the DMF the angular moment is decreased in front of the torsion damper and increased behind it. The angular moment of the engine is now assigned to the primary mass of the DMF, while that of the transmission is assigned to the secondary mass including the clutch driven
plate and the clutch pressure plate. In this way, the resonance speed is shifted from approx. 1300 rpm to about 300 rpm and can no longer interfere with driving comfort, as the engine is not operated in this speed range. An added positive effect is provided by the reduced angular momentum on the engine side: Gear changing is improved thanks to the lower mass to be synchronised, and the synchromesh units are subject to less wear. The effects on torsional vibrations can be seen from the diagram With previous conventional flywheels and torsion-damped clutch plates, the torsional vibrations in the idle speed range were transmitted to the transmission with the least possible filtering, causing the teeth of the transmission gears to strike against one another (transmission rattle). The use of a dual-mass flywheel however, filters out the torsional vibrations of the engine by the complex construction of the torsion damper, preventing vibration from affecting the transmission components - rattling does not occur, and driver comfort is fully ensured.

The advantages of the LuK dual-mass flywheel at a glance:
* first-class driving comfort
* absorption of vibrations
* noise insulation
* fuel saving due to lower engine speeds
* increased gearchanging comfort
* less synchronisation wear
* overload protection for the drive train"<ul><li><a href="http://www.luk-as.pl/pl/aktuell/download/pdf/luk_clutch_course.pdf">http://www.luk-as.pl/pl/aktuell/download/pdf/luk_clutch_course.pdf</a></li></ul>

Wrinkledpants

Great read. It's things like this that make me seriously consider a company's product.

Chaddy

thanks Dave, that's a nice find....for us nerds anyway

sj6sp

Yeah but, the (Luk) RS4 PP is still junk IMO :-)

Wrinkledpants

I think if you aren't launching (which I don't) then it's a great clutch if stock feel is important to you over launching. If you plan on burning rubber from every stop light, well then it's time to get a more beefy clutch.

sj6sp

It actually held up pretty well in that respect.

Mine failed not from slippage/wear but a finger snapped one day during normal driving and it would no longer release competely.
I don't think it snapped from torque either.

Check the archives...this has happened to a lot of cars running RS4 PP.

davenew

megafreakindeth

its common engineering stuff, there are pros and cons to everything. the heavier the object the more inertia it will store; the more vibrations it will store(low amplitude or high frequency especially). this will also reduce the back and forth sloshing between the gear sets. each gear has some play in it between the teeth and these will rock back and forth unloaded, this acts as a spring pushing more energy back up into the motor(hence why some driveshafts have some ability to slide in and out at a joint). having the springs in the flywheel also does a good job of dampening the shock from shifting with the heavier object rather than the relativly light clutch disc. also the car is easier to drive for stupid people with money as is the case for a great many sports cars. tons of people go out and buy a good performance car like this or better and cant even drive stick hence audi can make more sales by making it super simple to drive badly.

if anyone has ever owned or driven a golf/jetta its quite smooth and simple and pleasant to drive and overall having this bulky crappy 30-40lbs flywheel/clutch is annoying if you know how to drive.
It absorbs inertia, which is in turn, not going to the ground to speed you up. it is also pushing the car forward while braking gretly increasing your stoping distance and brake response time(hence the huge brakes, notice the non dual mass cars of later have smaller brakes yet work much better). it also keeps pushing even if your letting off the throttle just cruisng around making it have a wide and lazy turning feel, it probably even increases the turning radius at speed.
the heavy flywheel is doing the flexing when the clutch engages, this increases lag for the onset of power. while the flywheel is flexing this decreases the load on the motor, no load no boost. then WOOSH tons of load and boost which is the same reason lots of people hate turbochargers.

now if you put on an 12 lbs flywheel(almunium of course) with a six spring carbon kevlar clutch(no pucks) it would be slightly louder than a passat 2.8 which is hardly loud at all if at all. as soon as you stepped on the gas the puny ko3 turbos will surge to life with the throttle. if you let off the gas the car slows down on its own, saving your brakes from being warped(which is a very common problem on this car), decreasing your braking distance, increasing the effectiveness of the already enormous calipers; which saves you the need to get larger brakes(an option i could see with a stock setup). The overall weight reduction saves you gas, decreases frontal weight, and lowers overall cost. it can easily be justified just by the handeling benifits.

i plan on doing this, with a light weight battery(in the trunk), and a 4:1 center diff. i feel this would make a much better car a few minimal changes and alot of labor of course. then if possible use the v8 brakes which will weigh alot less. all totally mabye 60-70 lbs weight reduction in the front and a 10lbs or so increase in the rear, as some weight redistribution is also needed.

in a nutshell a dualmass setup would be best on something like the phaeton where comfort and grace is key

RolledMySTi

^^^yep.

I have light weight pulleys, lightweight flywheel, 034 track motor mounts and street tranny mounts. Car is smooth as can be. No rattles or bucking.