The Dual Mass Flywheel
Posted by murmini Sun, 01 Apr 2007 19:44:18 GMT
I recently suffered an intermittent rattling noise coming from the clutch assembly in the front, drivers side of the car and was fairly certain that it was the release bearing as it would disappear as soon as you depressed the clutch.
However, it was unusual in so much as once a release bearing becomes noisy it usually stays that way. So the fact that on many days it was completely silent seemed odd. I also occasionally noticed it increasing with engine temperature. It wasn't a deep concern as it was happening with such infrequency and of course it would never misbehave when it was at the dealership for service. Well finally it did and was diagnosed as fitting the exact criteria of a Technical Service Bulletin for 05 vehicles that had faulty dual-mass flywheels.Â
To me, the flywheel has always been a simple device - a large, flat metal plate about 3/4 of an inch thick that is bolted onto the end of the engine crankshaft. It has a toothed gear around its circumference that the starter motor engages in. Designed to give the engine momentum and to assist with starting, there is a machined surface at the point of contact for the clutch, which is held against the flywheel by way of the clutch assembly. A spring-loaded pressure plate connects the car's gearbox to the flywheel by compressing the clutch plate between the flywheel and the pressure plate, conveying the engine's rotational force to the gearbox and subsequently to the car's drive train and wheels.
The clutch plate itself (the part that wears) is made of a similar material to brake pads and, when your in gear and driving, is pressed hard against the flywheel by the pressure plate. As you depress the clutch, a metal ring assembly that is around the the drive-shaft is pressed up against the clutch assembly and it compresses the springs releasing the pressure on the clutch plate and prevents transfer of power from the engine to the gearbox. You can then change gear, or stop the vehicle, without impacting engine speed. This assembly is called the release, throw-out or thrust bearing. Here is a great diagrammatic example of how this works.
Modern engines are much more capable than ever before of being driven at low engine speeds. In fact the addition of a fifth or a sixth gear to reduce fuel consumption certainly moves towards having more torque capability at lower rpm. Also thinner gearbox oils and advanced gearbox design are making precise shifting easier. In short: The sources of natural damping is decreasing. More efficient gearboxes using lighter weight oils have greatly reduced the natural damping effect for both vibration and noise that older more stodgy drive-trains used to have. Our engines are still being driven with a four-cycle reciprocating piston stroke: Induction, Compression, Ignition and Exhaust (suck, squeeze, bang, blow) the crank shaft converting these vertical down thrusts from the ignition cycle to a rotational force at the flywheel.
The result, shown in this diagram, is a lot of vibration that is carried from the engine to the drive-train, particularly as the clutch engages and the vehicle starts to pull away.
The job of the clutch is now taking on another role. In addition to connecting and disconnecting the power from the drive-train, it must also prevent the transmission of the engineâs vibrations. One of the first manufacturers of a solution to this was the German company LuK. Here is a cut-away view of the Dual Mass flywheel used in the MINI.
The mass of the conventional flywheel was simply split in two. One part continues to be attached directly to the car's crankshaft in the same way as a standard flywheel would be, while the other part now increases the mass moment of inertia of the transmission. The two decoupled masses are linked by a spring/damping system. One clutch disc, between the secondary mass and the transmission, handles the engaging and disengaging functions.
A favorable side effect is that the transmission is easier to shift because of the low mass to be synchronized, and there is less synchronization wear. This greatly improves drivability by absorbing the vibrations, reduces noise and enables comfortable, low-revs driving and contributes to better fuel economy. One side effect is that the dual-mass does tend to have a resonant frequency that could contribute to noise so an additional damping device effectively prevents resonance overload. In normal operation, however, this additional damping device has no function and the torsional vibrations of the engine are filtered out by spring dampers. These damping springs are long, as can be seen in this illustration.
For optimal vibration isolation and soft resonance when starting and stopping the engine, the ratio between friction and spring rate must be optimal. The length of the springs is a key factor: The softer a spring, the more efficiently vibrations are isolated. The extra-long springs of the latest generation of dual mass flywheels significantly reduce the spring rate compared to a first generation dual mass flywheel. In routine driving operations, excessive resonance increases are kept almost completely away from the gearbox. The dual mass and the springs mounted sideways between the primary and secondary flywheels provides extra vibration dampening and eliminates excessive transmission gear rattle for smoother clutch engagement and operation. Dual mass flywheels were first used in the mid 80s on Chevrolet, Ford and GMC diesel-powered light trucks, and are found today on a number of trucks and even some European sports and luxury cars.
Well, its goes to show that the auto industry will never stand still when it comes to innovation and technological advances. Even things as simple a flywheels have advanced and now provide benefits beyond their original design. Since I had my dual-mass flywheel replaced the noise and rumbles have completely gone away.
I would like to thank the people at LuK GmbH & Co. oHG for providing me with these great illustrations and the permission to use them.
Also, there is an excellent animation here from the ZF transmission company.
Holy Cwap… is there going to be a test? Did it get fixed under warranty?
=:¬)... RB
First of all, let me say, EXCELLENT article.
Now, let me grind your synchros a bit..
You state: ”...the transmission is easier to shift because of the low[er amount of?] mass to be synchronized”
How so?
Is this something a DMF manufacturer claims?
When the clutch is depressed, the mass of the flywheel isn’t in play. You could have a five pound or a fifty pound clutch and it wouldn’t change how much mass was being synchronized.
Single or dual mass is irrelevant when you’re in the process of shifting and the disc isn’t engaged to the flywheel.
The only basis I can think of for this statement is that the removal of springs from the disc itself makes it somewhat lighter, and indeed, it is a mass that must be synchronized—along with that of the release bearing.
Thoughts?
Again, excellent article. Take this as a desire to understand better, not criticism, please!
Wade Nelson, Engineer/Writer
Wade: Thank you for your comments and compliments. I am delighted that you have raised this question. Yes, I have read of the synchronization improvements from DMF manufacturers and it begs the understanding of how different this would be, with or without a DMF. The assumption that a clutch plate, that weighs very little (particularly on the MINI Cooper S model as it has no integral springs) would have an insignificant impact on mass synchronization. However, manufacturers do claim this advantage point. It may be that they feel the DMF negates the need for the normal 4 springs mounted in the clutch plate, but I would have thought the actual weights involved to be minimal. If you want to explore the more empirical aspects of the DMF design and subsequent inertia issues, there is an an excellent white paper available from Luk, GmbH here. Thank you again – I am most grateful that you took such an interest in the article.
I, too have recently had the same clutch noise symptoms in my ‘06 MCS, now in addition to a drivetrain noise which occurs when the drive gears are “in float”, that is, neither accelerating nor deaccelerating, but just in between. Baffled as to exactly what it was, the dealer and I had previously amicably agreed that this was some kind of “gear lash” noise and that we’d take a watch and wait approach on the problem. I agreed that we couldn’t just start adding major drivetrain components without having a better idea exactly what the problem was. Recently though, a new noise developed, particularly on start up, a “tick-tick-tick” in neutral with the clutch out. The noise disappeared when the clutch was depressed. I returned the car to the dealer and yesterday learned that they’ll be replacing the “dual mass flywheel”. Realizing I really didn’t know what this kind of flywheel was and wondering what I could learn about the MINI’s, I turned to the Internet this morning and lo and behold, here’s your very informative thread. Thank You! It’s good to know I’m not alone. ;-) This MINI community continues to amaze me with its ability to disseminate good knowledge on our cars via forums and weblogs. Just a few weeks ago I was able to do a complete suspension swap out with step by step instructions provided on a forum. Fantastic! My greatest hope now is that the flywheel is also the root of this mysterious drivetrain noise and both of my woes will be “dually” corrected!
There is a good chance it is the DMF. Its quite a complex device and if malfunctionng, is likely to cause all kinds of odd sounds. Please let us know how yours works out and if the DMF replacement fixes it.
OK, the Dual Mass Flywheel has now been replaced and much to my surprise, the results are mixed. Upon picking up the car it seemed we had indeed solved both of the problems – no more “ticking” in neutral with the clutch out and more importantly to me, no more of the previously reported, mysterious drivetrain noise. So, clearly the DMF had been the culprit. The following morning I was less than amused to discover upon startup that the “ticking” noise had returned in a fresh new version, this time even more pronounced than than the original flywheel’s noises! You’ve GOT to be kidding I thought. How can a brand new, supposedly latest generation DMF do this? Mercifully the drivetrain noise had not returned so at least one of the problems had been slain. I stopped by the MINI dealership later that day to chat with the shop foreman who’d done the work. While he obviously hadn’t heard the noise during the post job check out, he actually seemed almost nonplussed that the new flywheel was no better than the one replaced. To his credit, he was and is more than willing to install yet another DMF at any time. Frankly, the impression I get is that the machanics are equally baffled by the rather quirky and unpredictable performance of these flywheels. He even jokingly remarked that perhaps the replacement had been “built on a Monday”! (rimshot!) He also remarked that he’d even heard some higher mileage MINI’s “that you’d think you were standing next to a diesel”, the noise was that pronounced. On the side of reassurance he stated that he was not aware of any of these DMF’s catastrophically failing and leaving anyone stranded. One other supposed factoid: MINI’s DMF, does NOT have the above described internal springs, but rather some type of rubber internals that perform the shock absorption. I’m a little surprised by this as in my mind I can more likely see how those “springs” would be a probable culprit of these types of noises. MINI definitely has a bit of a problem here with these DMFs, but I’m not sure the problem, at least currently in management’s minds, rises above the level of being more than an inherent noise that is somewhat of an aesthetic quirk that can be lived with for the time being and, if need be, can be replaced under warranty on a per case basis. Time will tell.
Clearly, for me, the “ticking” is an annoyance and obviously unacceptable on a car of this caliber and it is my intention to soon throw the dice again on a third DMF. Stayed tuned for more in this continuing saga of the DMF!
Very interesting – I too will do a little research. Thank you very much for informative posting. Please let me know how things work out with DMF 3.
Interesting article. The GM duramax diesels with 6-speed transmissions have had the same problem for years with their Luk Dual Mass Flywheel. I have a new DMF on order from the dealer right now with only 29000 miles on the truck. If you go to www.dieselplace.com and browse the “ZF-6 OEM” forum, you will see many stories regarding the DMF rattles with numerous replacement stories, two or three on one truck. So it’s very interesting the the Mini Coopers are having the same problems. Sounds to me like Luk doesn’t make a good DMF. Goodluck
Good article.
I have a Peugeot 307 2.0 hdi, second hand. Also I bought with it a squeal noise coming from the engine, which gets louder every month. Didn’t hear it at the time of buying. I had 15000 km with it last year. Recently, mechanics found out that the noise comes from DMF. The cost of the repair is huge, about 1100 euro. Pretty annoyed with the car and the LuK now. Total amount of km – 46000 only!
It is general knowledge in VW that the DMF can catch fire
Update: 52000km, still squealing but still going.
Sasa, I have had no further trouble with my DMF, but the new clutch plate that was installed when the flywheel was changed, squeals occasionally as I pull away in first. I am approaching 55k miles.
Just a comment from an older guy who has owned & driven nearly 100 cars from 1958… I get bemused when I hear of all this trouble with modern motors simply because of over-complexity. Push-rod engines had NO snapping cambelts causing thousands of pounds damage. Flywheels were just a big lump of machined steel, they COULDN’T go wrong. ECUs costing half a grand to replace? NO! Petrol injection? A well set up S.U. carb. and manifold—just as good. Average mpg. of a Morris Minor 1000? About 50mpg. Modern high-performance cars? Tell me about that as you’re sitting in that endless traffic jam! Someone will get back and say about pollution, and I agree regards tetra-ethyl lead in petrol, but it wasn’t hard to make an old fashioned engine work on unleaded. Carbon monoxide? Fuel injection makes very little difference, but I will agree variable valve timing does by getting nearer to the stoichometric ratio at idle & low-load. And what is the financial saving of all these so-called improvements when one bill alone for a dual-mass flywheel can be £1000? In 1970, if you said “economic write-off” to a car owner, he wouldn’t know what you were talking about. Neither would he understand “cosmetic write-off”. I think we have been bamboozled by a big load of unnecessary legislation about our cars; car makers have done their best in some respects, but there is the cost problem to make cars reliable with all this frankly over-complex technology. If all the new euro-legislation come about, no-one will be able to afford to use a car, or even park it anywhere!
i have a 94 f350 my dmf just discentegraded on my vichle having aproblem finding one under eight hundred dollars
LuK, manufacturer of the dual-mass flywheel, has issued a “white paper” about the unit, which is extremely interesting if you are technically oriented. It may be discovered by delving into their website: www.luk.de and searching for the:
“7th LuK Symposium” paper, held: 11.12. April 2002
I am having a problem with my clutch that only occurs after being stuck in stop and go traffic for a while and only with 1st gear. It starts to rattle the whole car as I am letting out the clutch and starting off. It feels like it is coming from the drivetrain, but it is strange that it ONLY happens in 1st gear. I do not have the problem if I start in 2nd.
I had the same problem in the 97 wrangler that I used to have. In the wrangler, however, the problem was much worse, and I didn’t have to be stuck in traffic for it to happen.
I was just wondering if this is the same problem that many other people were having. Is this something that I can take to the dealer and have it fixed under warrenty? Please advise. Thanks!
Matthew: These things are almost impossible to diagnose without hearing it. It sounds like it is fairly repeatable and yes, you should take it to your dealer and have them go for a run with you. Let us know what transpires.
I’ve recently bought a second hand VW Passat TDI 97kW( year 2005) and I am investigating my problem for the last 3 months, finally I’ve got a hint that source of my problem can be a DMF (after eliminating compressor, PD ignition…). When I a driving at a 1800 rpm ( 4 gear, 60 km/h)a car start to shaking (very good visible at a gear box rod), if I reduce the rpm to 1400 or increase to 2000, shaking disappear. I was told that possible springs in DMF become “soft” at shaking are the result of faulty DMF. What do you think? How to diagnose DMF more exactly?
Well of course it is possible, however my own experience and that of MINI owners, tends to be while the car is stationary and the rattling/vibration taking place as one depresses and releases the clutch pedal. That said, anyone with anything to add please chime in.
Hi Jurij, I used to have a Jeep Wrangler that would have a similar problem. You might want to get your wheel alignment checked, once I had my wheels aligned, the shaking went away
Hi,
Valeo has launched a product that replaces the DMF with a rigid flywheel+ dampen type clutch kit. It eliminates the clutch problems on Mini and provides better comfort
Tkns for your interesting article on the DMF.My 2nd hand GOLF GTI with only 18000 mls on its clock has developed some noise & vibration mostly felt on taking off from rest -or when stopped if you lightly brush the accelerator pedal & just touch the clutch pedal,you can feel the viberation through the clutch pedal! Its not very bad but makes itself more evident during a lot of stop-start driving.My local VW dealer says this is an accepable amount of noise from the DMF,and if he were to replace it the new one will most probably be the same! Up to now i never knew what a DMF was,or what its function is and the small animation clip on your site has been a ‘great help’ at least i can see now whats going on and i suppose understand where some of the noise is coming from. I just can;t understand why a clutch manufacture can design something like this and after a small amount of careful driving it goes pearshaped!I suppose it has its advantages in that the clutch and gears are always smooth in operation but when noises start to creep into a very expensive car,and after such a small milage it makes you think do the car manufactures ever do long term tests on their cars?
a Morris 1000 will not average 50mpg and fuel injection produces far less monoxide. Please enough of this good old days nonsense.
Mark, I have to agree with you. I too share a rather nostalgic view of older motoring technology and have spent much time ‘tweaking’ SU and Stromberg carburetors and setting dwell angles on old Lucas points. However, the modern motor vehicle is quite a remarkable piece of technology. One only has to take even a cursory view of the workings of a modern Engine Control Unit to appreciate the efficiencies and reduced maintenance that they bring.
The Morris Minor 1000 claimed a fuel consumption of 38 miles per imperial gallon, but one has to consider its curb weight of 1679.92 lbs. compared to a MINI Cooper of today, with a weight of 2660, nearly 1000 pounds more, much of which is safety equipment and improved protective technology.
One must appreciate and applaud the pure nostalgic elements of where automotive technology has come from. I do, however relish the fact that every time it rains, I don’t have to jump out of my MINI and make sure I have a plastic bag over my distributor cap.