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

[k.udhay]

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.

 

[Tom.G]

You may have noticed that the damper springs in the DMF are much longer than in the SMF. Also in the DMF, most of the flywheel mass is in the second flywheel.

This allows a much lower spring constant (higher compliance) of the damper springs, and consequently better decoupling the engine rotational variations from the flywheel/drive train.

EDIT: As an example consider a jug of water suspended from you hand with a rope (the SMF damper springs) versus suspended with a long rubber band (DMF damper springs). If you rapidly jiggle your hand up and down using the rope, the jug will follow. If you use a rubber band, the jug will not move as much.
end edit:

 

[jack action]

1. What difference does it make by doing the above changes?

You basically move the mass moment of inertia (MMoI) from the engine side to the transmission side.

The engine rpm is varying, but what you really care about is that the transmission rpm is stable. Increasing the transmission MMoI will do that. Transferring mass from the engine side to the transmission side, means you don't have to increase the total mass.

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.

Inertia is more than mass; You have to consider the radius too. The further the mass is from the center of rotation, the greater the MMoI.

So, to increase the MMoI of the transmission by increasing the input shaft mass (close to center of rotation), you would have to have a greater mass than what you would remove from the engine flywheel (located at a larger radius). This would result in an increase in total mass.

 

[k.udhay]

You may have noticed that the damper springs in the DMF are much longer than in the SMF. Also in the DMF, most of the flywheel mass is in the second flywheel.

This allows a much lower spring constant (higher compliance) of the damper springs, and consequently better decoupling the engine rotational variations from the flywheel/drive train.

EDIT: As an example consider a jug of water suspended from you hand with a rope (the SMF damper springs) versus suspended with a long rubber band (DMF damper springs). If you rapidly jiggle your hand up and down using the rope, the jug will follow. If you use a rubber band, the jug will not move as much.
end edit:

Lovely example, Tom! So glad that I posted the question here. Thanks a ton!

 

[k.udhay]

You basically move the mass moment of inertia (MMoI) from the engine side to the transmission side.

The engine rpm is varying, but what you really care about is that the transmission rpm is stable. Increasing the transmission MMoI will do that. Transferring mass from the engine side to the transmission side, means you don't have to increase the total mass.

Inertia is more than mass; You have to consider the radius too. The further the mass is from the center of rotation, the greater the MMoI.

So, to increase the MMoI of the transmission by increasing the input shaft mass (close to center of rotation), you would have to have a greater mass than what you would remove from the engine flywheel (located at a larger radius). This would result in an increase in total mass.

Thanks for giving a detailed answer, Jack. So we prefer to add inertia in clutch side instead of T/m as clutch can allow mass addition at a higher radius practically.

 

[Dana Kasymbabina]

Our department of technological equipment, engineering and standardization at Karaganda State Technical University deals with these researches http://www.kstu.kz/