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

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Discussion Overview

The discussion centers on the differences between Dual Mass Flywheel (DMF) and Single Mass Flywheel (SMF) clutches, focusing on their construction, functionality, and implications for engine and transmission performance. Participants explore theoretical and practical aspects of these flywheel systems.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note that DMF construction involves splitting the flywheel mass into two pieces, incorporating damper springs, and assembling the clutch plate to the secondary mass, which may enhance performance.
  • One participant suggests that the longer damper springs in DMF allow for better decoupling of engine rotational variations compared to SMF, using an analogy of different suspension systems.
  • Another participant explains that moving the mass moment of inertia (MMoI) from the engine side to the transmission side can stabilize transmission RPM, arguing that this transfer does not require an increase in total mass.
  • There is a discussion about whether simply increasing the transmission input shaft inertia could be equivalent to DMF construction, with some arguing that the radius of mass placement affects the effective inertia.
  • One participant emphasizes that to achieve the same MMoi effect by increasing input shaft mass, a greater mass would be needed compared to what could be removed from the engine flywheel, potentially increasing total mass.

Areas of Agreement / Disagreement

Participants express differing views on the equivalence of increasing transmission input shaft inertia to DMF construction, indicating that the discussion remains unresolved regarding the implications of mass placement and its effects on performance.

Contextual Notes

Participants highlight the importance of considering both mass and radius in discussions of inertia, suggesting that assumptions about mass distribution and its effects on performance may not be fully resolved.

Who May Find This Useful

This discussion may be of interest to automotive engineers, mechanical engineers, and students studying mechanical systems, particularly those focused on drivetrain dynamics and flywheel technology.

k.udhay
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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.
 
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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:
 
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k.udhay said:
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.
k.udhay said:
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.
 
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Tom.G said:
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!
 
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jack action said:
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.
 
Our department of technological equipment, engineering and standardization at Karaganda State Technical University deals with these researches http://www.kstu.kz/
 
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