Dual Mass Flywheel (DMF) Description and Function
 

<center><img src="http://pictureposter.audiworld.com/15624/dualmassflywheelx-sec.jpg"></center><p>
What is the DMF's function? It is designed to isolate torsional crankshaft spikes created by high power, high torque engines including diesel engines with high compression ratios. By separating the mass of the flywheel between the engines and the transmission, torsional spikes can be isolated, eliminating potential damage to the transmission gear teeth. There are several components:

[IMG}http://www.lukclutch.com/images/flywheels/page04_a.jpg[/IMG]

Engine-side flywheel damper springs: The damper springs that are visible on the engine side of DMF are designed to dampen heavy torsional spikes that occur when the engine's torsional frequency matches the torsional frequency of the transmission. When torsional frequencies match (have the same amplitude), severe damage can occur to the transmission if not isolated. DMF's isolate the torsional frequency match between the engine and transmission to an r.p.m. range below the operating range of the engine (usually between 200-400 r.p.m.). These damper springs only work hard when the engine passes through 200-400 r.p.m. at vehicle start up and shut down.

DMF damper springs and/or damper springs nylon retainers usually fall because the engine is not running correctly. Bad fuel injectors, worn pistol rings, bad valves, etc, will change the resonant frequency of the engine. A change in the resonant frequency of the engine can force the torsional frequency match between the engine and DMF to fall within the operating range of the engine. This forces the damper springs to work continuously, resulting in failure.

Friction Ring: The friction ring located between the inner and outer flywheel is designed to allow the inner and outer flywheel to slip. This feature saves the transmission from damage when torque loads exceed the vehicle rating of the transmission. (Read: Burnouts/high RPM shifts) The friction ring will wear out if excessive torque loads are continuously applied. Loading the vehicle beyond the rated load capacity is often the root cause of friction ring failures in DMF's.

Center Bearing: A sealed double row center ball bearing carries the load between the inner and outer halves of the DMF. The leading cause of center bearing failure is often related to out of balance vibration caused by not aligning the pressure plate with the DMF dowel pins. The center bearing may also fall if the clutch pilot bearing is destroyed by a worn transmission input shaft (see Pilot Bearing) or if the rated load/towing capacity of the vehicle is exceeded.

Pilot Bearing: The pilot bearing supplied with most DMF's is a caged needle roller bearing. If it fails, the transmission input shaft must be repaired or replaced. If the input shaft is not repaired correctly or replaced, the lack of input shaft support will result in DMF center bearing failure.

good read.

I read it, I'm not sure what it all means, but cool. :-)

questions
 

The pic implies that the mass are unequal. Is is this true? and what dictates the Mass of each. Is there some sort of ratio that must be maitained. What would a symptons be if these masses were changed?

It means the stock flywheel is designed to a) reduce vibrations and b) save your tranny from...
 

shocks. IMHHEO, going to a non-dual mass flywheel could be bad for the tranny.

No idea. I think the important part is the fact the there are springs between the two masses to...
 

help take up vibrations and torque shocks (to a point when the springs are fully compressed).

I think.

;&gt;)

Ohhhh, ok. :-)

nice read. I was wondering,because on other forums i have seen that dual mass flywheels say have a limit to power,is it possible to know how much that is and why?

My mechanic seems to think that it is better for higher power,even if it is heavier than those aluminium flywheels.

cheers
vasilis

I'm not sure how much power the DMF in the UrS can stand up to, but it makes sense that a DMF could have issues with increased power. A DMF is made up of 2 basic parts that can move independently to absorb shocks/vibradions from the engine and prevent them from damaging the trans. If you increase the amount of power being transfered through the flywheel there will be a point that the springs will not be able to hold the increased power and will fail.

A single mass flywheel is a solid piece of steel or aluminum with no moving parts to wear out or break.

i was wondering if it is the abrupt increase of torgue that will cause damage to the DMF or the total amount of torgue/power produced in general.

Im currently running a DMF with the GT3071R setup and according to calculations im at around 530-560Nm of torgue crank.Im going to try about 500hp crank(now around 420-425) with i would imagine about 600-620Nm or torgue.Im going to be introducing boost gradually and then holding it to the red line,so there will be less stress on everything basically.