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DMF dual mass flywheel


Michael RAV4
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Yeah DMFs are a really daft invention. AFAIK none of the Aygos have a DMF, and the only Yaris models with DMFs are later models of Mk2 diesel and onwards - None of the petrol ones have!

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2 hours ago, Cyker said:

Yeah DMFs are a really daft invention. AFAIK none of the Aygos have a DMF, and the only Yaris models with DMFs are later models of Mk2 diesel and onwards - None of the petrol ones have!

they make sense on turbodiesels - they protect the driveline from high torque at low rpm.

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Some petrol cars with turbo engines has DMF too, smoother clutch operation.  CVT transmissions has a torque converter that usually play the role of a clutch and DMF, some DSG auto gearboxes from vw has DMF + two dry clutches but others has a torque converter and wet clutch packs plus two separate Oil circuits., more things to go wrong in comparison with eCVT transmissions in Toyota/Lexus hybrids. 

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11 minutes ago, TonyHSD said:

Some petrol cars with turbo engines has DMF too, smoother clutch operation.

Most of the VW Group current turbo petrol engines have a DMF - certainly all the current Skoda Octavias and VW Golfs do.

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1 hour ago, Heidfirst said:

they make sense on turbodiesels - they protect the driveline from high torque at low rpm.

Actually they don't, not specifically anyway - Heavy flywheels do a much better job of absorbing the high torque pulses of a diesel engine, and is why most diesel engines have heavier flywheels than equivalent petrols. The DMF was specifically created to reduce emissions (and also improve fuel efficiency and accelerator response as a side effect), by allowing the use of a much lighter flywheel while still being able to absorb large torque pulses.

Unfortunately, at least as far as I'm concerned, it is a total failure - The DMF is just incapable of absorbing the high torque pulses of diesel engines in the long term: The hammering action of the torque pulses against the spring stops under high load and the springs themselves acting as sandpaper against the casing just makes them a very expensive wearing part.

Prior to DMFs, I'd very very rarely heard of a flywheel failure and it would often last the life of the car, but with DMF-equipped cars you are often recommended to replace the DMF when you replace the clutch; In fact earlier implementations the DMF would often fail before the clutch disc wore out!

This has mitigated in more modern vehicles, and DMFs now tend to have a longer life span, but not because they have been improved significantly - Instead almost all manufacturers started electronically limiting the torque curve of their high torque diesels to be gentler on the DMF because they had such a high failure rate. But why not just use a slightly heavier solid flywheel and do the same thing?

Personally I would much rather have a car without a DMF - They don't give enough advantage over just using a heavier flywheel, but increase cost and reduce reliability significantly (SMF - £~150 and rarely needs replacing; DMF - £>500 and guaranteed will need replacing!). I'd rather not worry about hearing that dreaded rattling sandpaper sound that signals an impending DMF failure!

 

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