Dual mass flywheel clutch - How does it make a difference? 1

[namelessudhay]

I was going through these two documents:

https://www.schaeffler.com/remoteme...effler_2/symposia_1/downloads_11/4_DMFW_1.pdf

http://www.partinfo.co.uk/docs/140

My primary interest was to understand why and how Dual Mass Flywheel (DMF) is superior over the conventional Single Mass Flywheel (SMF) clutch.

DMF undergoes three major differences in construction:
1. Flywheel mass is split into two pieces - Primary mass and Secondary mass
2. Damper springs are fitted to the primary mass
3. Clutch plate is assembled to secondary mass

These are my two questions:
1. What difference does it make by doing the above changes?
2. If I just increase the transmission input shaft inertia, is it not mathematically equivalent to the DMF construction? Because, the core change in DMF is that there is a mass after dampening. Pl. help.

 

[BrianPetersen]

We are talking manual transmission here.

A normal manual clutch assembly (one meant for use with a normal solid flywheel) contains a vibration damper inside the friction plate - the same type of arrangement transmitting the torque through springs that a DMF uses.

The DMF-style clutch assembly has a solid friction plate.

So what it amounts to is that the vibration damper has been transferred from the friction plate "downstream" of the engagement location, to the flywheel "upstream" of the clutch engagement location.

The difference ... is that the DMF arrangement keeps the vibration damper in the system at idle when the driver has their foot on the clutch pedal.

VW diesels switched to the DMF design with the Golf Mk4 generation in order to reduce noise and vibration at idle. You can retrofit the earlier single-mass flywheel (and the clutch assembly that goes with it) to the later models ... they'll rattle a little bit more at idle. In that particular case, it's done because there is better aftermarket support for the single-mass-flywheel clutch design and they're more durable in the long term.

There is no flywheel on the input shaft of a transmission. The moment of inertia of the input shaft is a tiny fraction of that of the flywheel and crankshaft of the engine. Adding inertia would do nothing to soak up the torque pulsations and reversals inherent in the crankshaft rotation of any piston engine ... particularly an even-firing inline-4 (which inherently has two increases and decreases of instantaneous crankshaft speed on every revolution!) diesel (19:1 compression) turbocharged (big compression and power stroke twice per revolution)! There has to be something to transform those twice-per-revolution hammer blows into something resembling smooth torque delivery, and that's why that spring mechanism has to be there somewhere.

 

[namelessudhay]

Thank you very much, Brian. I understand if there was no secondary mass, the dampening of spring would not be efficient at high slip condition of the clutch.