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Dual Mass Flywheels - What and How

 by james on 07 Mar 2012 |
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This week I've sold two dual mass flywheels, so I thought it might be worth explaining what they are and how they work, and how they differ from a “regular” or single mass flywheel and how they work.  As you will see, these concepts are all closely tied up with one another.
First, some basics: what is a flywheel?  A flywheel is a store of energy.  It’s an intentionally heavy circular lump of metal that is bolted onto the end of the crankshaft.  It’s main function is to even out the power pulses from an engine.  When the first cylinder fires, it has to overcome the inertia of the flywheel, but after the first cylinder has fired, the momentum of the flywheel keeps the engine turning over.  As with pretty much everything in engineering, there is a compromise going on: a heavier flywheel makes for a smoother feel, but a lighter flywheel spins up faster, and so allows an engine to feel friskier and more responsive.
That’s a flywheel explained in one paragraph.  Now for the dual mass flywheel.  The two masses in a dual mass flywheel are joined to one another with springs, and one part of the flywheel can rotate independently of the other, until the limit of the springs.  Now when the first piston fires, part of the flywheel is spun, but the second, sprung part, does not move at first.  It’s that inertia thing again.
As the first part of the flywheel slows down, the sprung part of the flywheel carries on moving towards it, and delivers its stored energy in a pulse, slightly later.  So, in simple terms, a flywheel stores energy from the engine, and a dual mass flywheel partitions that stored energy up, and releases it in two smaller lumps, instead of one big one.
And, wouldn’tcha know it, we now have another compromise going on, because to get that level of sophistication, and an even smoother engine feel for a particular weight of flywheel, we now have a flywheel which has moving parts which can wear out instead of being just a dumb lump of metal.  (And yes, in most cases, a solid flywheel conversion kit is available for cars which were sold with a dual mass flywheel.)
Finally, there is another function that a flywheel performs and that is to provide a surface for the clutch friction plate to act against, and this another area where flywheel mass makes a difference, because a heavy flywheel, with lots of inertia makes for a clutch that is easier to pull away smoothly without stalling.  The compromise: a lighter flywheel, which will require more revs and a deft feel to pull away smoothly also makes for a car that will accelerate better, because there is less rotational inertia to overcome.


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All pictures and references to the brands and logos are for reference only, and do not imply any association with the brandholders. Most parts offered are OEM or quality aftermarket parts.  Genuine Porsche or MINI parts are specifically identified as such.  Master Parts  is not responsible for any typographical errors contained within the site.   Information within this website is for reference only.   It is your responsibility to verify that you are technically competent to carry out repair and maintenance procedures.  By entering this site, you agree to hold Master Parts free from any liability arising out of the use of any information contained within.
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