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Harmonic dampers

Harmonic dampers

(OP)
I guess while I'm here I'll throw up another idea that's been on my mind. Pendulum style harmonic dampers.
http://www.dragzine.com/tech-stories/engine/tcis-r...


There are a lot of solid crank pulleys out there. Often used to reduce weight. There is also a lot of good info out there that suggests it's not a great idea to use them because they can cause added stress, harmonics and on some motors even very rapid failure. Now all the 4 cylinders I deal with are naturally balanced so we don't have to worry about harmonic balancers like some motors do, just the harmonic dampening that helps prevent harmful frequencies from increasing to a dangerous point.
I am developing a pulley that has an integrated trigger wheel and I would like to use a solid pulley as it will be much cheaper to make. I have also read mixed reviews on polymer dampers especially when building high performance motors because from what I can tell they are designed primarily for one frequency range and from what I understand the harmful frequencies can change as you change things on a motor like displacement, horsepower, RPM, Boost, etc.
If I could get a pendulum style damper to work it seems like it would be pretty perfect for what I'm trying to do. I would assume that any weights would help dampen these frequencies but in that article they make it sound like it takes a specific design to work with different motors. It has me wondering if this is a huge issue or something they emphasize to scare people away from adopting it. My main question is whether it would be possible for a design like this to actually amplify frequencies if it was the wrong diameter or weight? Or would it just work less well?
Some day I would love to actually make a few designs and test them monitoring crank speed with a fine tooth trigger wheel or something but that won't be happening any time soon.
Do you guys have any thoughts on this? Would some weights even if not ideal be better than a solid pulley? Or could it be possible for the wrong design to actually be worse than a solid pulley?

RE: Harmonic dampers

The system shown in the magazine article reminds me of some piston engine aircraft cranks where the weights are fitted into the crank counterweights.

"Or could it be possible for the wrong design to actually be worse than a solid pulley?"

I think it is always possible to make things worse. That's a law of the Universe. Especially with tuned vibration absorbers and dampers. But, there are some non-tuned systems that simply dissipate vibrations through friction. These should always help, but they may absorb a lot of heat.

RE: Harmonic dampers

(OP)
Yeah from the research I did it sounds like this has been common in aircraft engines but not so much in automotive.

RE: Harmonic dampers

all the 4 cylinders I deal with are naturally balanced so we don't have to worry about harmonic balancers

Harmonic balancers are used for damping torsional vibrations. "Natural balance" has no effect on TVs. Short crankshaft is the main reason most 4cyls do not suffer.

je suis charlie

RE: Harmonic dampers

hI yoshimitsuspeed ,

You said -
"Some day I would love to actually make a few designs and test them monitoring crank speed with a fine tooth trigger wheel or something but that won't be happening any time soon.
Do you guys have any thoughts on this? "

==========

Measuring at one location might just show speed variation.
At big throttle an infinitely stiff crank would still respond to Fig 2 here
http://lh6.ggpht.com/_Ii1ukGkfijY/SpGk6BZ4HyI/AAAA...

I believe you'd need to measure at both ends of the crank and precisely consider phase to detect torsional vibration (twist).

RE: Harmonic dampers

(OP)

gruntguru
I was always under the impression that counterweighted pulleys were just used on motors that were not naturally balanced. I will say I never looked into it much as I have never messed with motors that did use counterweights. It doesn't seem like counterweights would be a good solution for torsional vibration since it will be stronger at some RPM than it will at others.

Tmoose yeah my thought was to just measure acceleration. Yeah you would have the baseline acceleration curve that you would have to work around but my thought was that it should still tell you if one design was better than another or if another was significantly worse. You are right that measuring at both ends would be much better and one thought I have had that would be pretty easy is putting a seonsor on the flywheel teeth. Then a fine tooth sensor on the front of the motor and you would be able to compare positions.

RE: Harmonic dampers

True you can measure crank accelerations and see some torsional variations, but measuring both ends, and in several other places if possible, can show you more. In most oscillating flexible systems there exists nodes that may show no or very small oscillations.

RE: Harmonic dampers

The end of a shaft is never nodal. The response at the flywheel end is reduced,but it is not nodal. In practice on automotive engines the first torsional mode is the only one of interest, for which the crank nose is antinodal.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Harmonic dampers

Quote (gruntguru)

I was always under the impression that counterweighted pulleys were just used on motors that were not naturally balanced.
Not necessarily. On the old school V8s I'm somewhat familiar with, they frequently resorted to counterweighted front balancer and flywheel/flexplate (i.e. external balance) on the large displacement variants of a given family, in order to maintain a common crankshaft with the smaller bore (hence lighter pistons) variants with common stroke, or in the case of longer stroke cranks, to conserve mass and rotating inertia by moving the balance mass out to the ends where you get most bang for the buck.
I think the long stroke crankshaft case is more common than the different piston mass per bore size - I believe it was not uncommon to maintain the same piston mass across different bore sizes (not optimum from a structural efficiency/margin standpoint!), in order to commonize the crank, balancer & front damper regardless of bore.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: Harmonic dampers

Speaking of harmonic dampers, I had a 1955 Olds 324 that I rodded with all the parts I could get my hands on, incidentally raising the peak operating speed to more than 2000 rpm higher than intended in factory tune. In hindsight, I probably needed an upgraded damper, not to mention full prepping of the cast iron crank. I chalk these oversights up to ignorance/inexperience; anyway, the end result was a fatigue failure in the web between cyls 2 & 3.
Had I known better, I would have desperately sought a steel crank and upgraded damper that must surely have been part of Old's contemporary "special heavy-duty" or "special export" parts list which existed in support of NASCAR racing, in which Olds was a strong contender from 1949 thru 1955, and had a brief resurgence in winning the 1959 Daytona 500, if I'm not mistaken.
In the event of failing to locate the factory racing parts, an alternative approach would have been to improvise the best I could, e.g. full prep on the crank, and adapt a herky aftermarket damper.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: Harmonic dampers

A "counterweighted pulley" and a "harmonic balancer" are two different things.

je suis charlie

RE: Harmonic dampers

(OP)
Okay well these motors don't use counterbalanced pulleys so what about damping? For now would it be safest for me to design a solid pulley with no damping? Or would there be any way to incorporate this pendulum style into my build being confident that it would be at least better than having none at all without doing a ton of R&D on it?

RE: Harmonic dampers

I'm not even sure what kind of vibrations you are getting. Your priority right now should be illustrating the vibrations to us with data.

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

RE: Harmonic dampers

(OP)

Panther140
The stock crank pulley has a bonded rubber damper.
I haven't studied these harmonics myself but there seem to be enough to make Toyota and all other OEMs I have seen choose to do this over a solid pulley.
Now on the 4AGE many people have run solid aftermarket pulleys without any issues that could be directly attributed to it so that is comforting. I have heard of some motors that seem to be affected much worse much sooner. The question still remains whether it might have any long term effect. Maybe they had bearing failure at 150k miles when the motor would have otherwise gone over 200k. That is not the type of thing that anyone would really tend to link when their motor lets go.
My plan is to make this solid crank wheel with integrated trigger wheel but if there is anything that I can do without investing a ton of time or money into it that would help then I would like to do that.
I do realize it would be hard to do something guarenteed to help without that large amount of R&D but that's why I'm here. To see if there is anything that I could do relatively quick and easy that should at least be better than nothing.

This article does a pretty good job of summarizing my concerns with solid pulleys.
http://www.atiracing.com/products/dampers/damper_d...

RE: Harmonic dampers

Oh I see now. A pendulum type dampener would help greatly with the issue of torsional vibration in that case.

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

RE: Harmonic dampers

Some straight fours do suffer quite badly from TVs - with "hotted-up" Morris A-Series 1100s you were advised to stay under or over about 6,000 RPM - but keep away from 6,000RPM itself where the TVs could break the crankshaft.

RE: Harmonic dampers

(OP)
Panther140 I do agree but the big question is whether there is a safe way of implementing something that should be better than nothing or if there is a chance that without a lot of R&D if it would be possible for the design to actually be worse than nothing.

BigClive Do you know if anyone ever managed to eliminate the issue with any type of dampening or other solutions?

RE: Harmonic dampers

The Cooper S and other higher performance models used a conventional rubber-and-metal damper.

RE: Harmonic dampers

Pendulum dampers are actually absorbers.
They cancel the torsional vibration of an order. That is the frequency they counteract is proportional to the speed of the shaft.
They have been used extensively in aerospace. Recently we have used them in Dual Mass Flywheels.

RE: Harmonic dampers

3
The steel inertia ring on rubber is a spring (the rubber or polymer) and a mass (the inertia ring) set up that is tuned to absorb torsional vibrations of a specific frequency.

The pendulum damper uses the centrifugal force owing to the rotation around the crankshaft axis as a “restoring force” returning the pendulum mass to the point furthest from the axis. This force varies with the square of the rotating speed. This variation in restoring force contrasts to the rather constant spring or restoring force of the rubber mounted ring.

FeX32 is correct, a pendulum damper is tuned to absorb energy at a multiple of the crankshaft speed. This multiple is commonly referred to as an ‘order’. (The third order is three times the number of crankshaft revolutions.)

The presence of damper on the original engine strongly suggests that the design engineers determined that there was as speed at which the combination of drive train inertias (not just the engine components) and the relative flexibility of those components in torsion resulted in excessive crankshaft torsional vibration or twisting.

By excessive torsional vibration we usually mean a twisting moment that results in a fatigue failure of the crankshaft or some component in the driveline.

Please know that the specifications of the damper were not chosen arbitrarily. A random selection of components is unlikely to result in an improvement in vibration damping. The calculations require considerable amounts of data and measurements not easily performed.

Without the damper, the engine will rev faster and some racers may choose to remove the damper for this reason. If the engine does not spend much time in the critical rpm they may get away with this practice.

The most comprehensive reference is “A Handbook of Torsional Vibration” published by Cambridge University Press in 1958. It is a collective work by the British Internal Combustion Engine Research Assn. (B.I.C.E.R.A.). Luckly for engineers everywhere, the book has been reissued recently in paperback and is available for about 40% of the original price from the same publisher. Regrettably, the only thing not included in the reissue was a nice foldout with a compilation of formulas for pendulum dampers.

RE: Harmonic dampers

Thanks for the good reference EHudson.
Other than the text "A Handbook of Torsional Vibration" do you recommend any others? Certain SAE papers of other texts?

Regards,

RE: Harmonic dampers

"Mechanical Vibrations" by Den Hartog is a personal favorite. There is an excellent introduction to engine vibrations dealing with vibrations from the reciprocating components and also the torsional vibration of crankshafts.

The subject of crankshaft torsional vibrations is not for the average casual reader of automotive literature. Den Hartog's book is about as easy a read as it gets.

I was blessed to have Prof. John C. Georgian, an old Nordberg diesel torsional analyst, as an instructor - otherwise this area of study would have been omitted from my engineering studies.

RE: Harmonic dampers

Thanks EHudson and Greg.

Part of my day job deals with torsional vibration isolation. I am curious about others experiences and references.
I am amazed our best reference of the theory comes from '58. I would have thought some new tech. would have come up. Although, the fundamentals will never really change.

Greg, you recommend "Practical Solution of Torsional Vibration Problems" ?

RE: Harmonic dampers

Thanks Tmoose.
Indeed there are lots of papers on SAE. I am a member.
I was curious about other references as well.

RE: Harmonic dampers

I only read Ker Wilson once, a long time ago, but I really liked it. Innovations I've seen in harmonic dampers in the last 30 years, practically zero, although the introduction of crankshaft bending dampers has become more widespread. At least one company allows you to tune bending and torsion separately by curving the elastomer element, which changes the bending frequency whilst leaving torsion unaffected.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Harmonic dampers

An alternative to doing all the design calcs to tune a damper (whether pendulum or elastomer) to the critical speed of your engine, is a viscous damper. These will work at any frequency where TV's rear their ugly head. This is because they are a true "damper" without their own spring-mass system and associated natural frequency.

je suis charlie

RE: Harmonic dampers

Have you seen comparative performance plots? Incidentally you can tune TV dampers by ear, a box of parts and a lazy afternoon will do it. The downside is that the audible tune is slightly different to what the engine people want, they tend to go for a lower peak frequency to get (slightly) more low frequency attenuation, whereas obviously by ear you hit the peak.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Harmonic dampers

Interesting. I have not seen much of the pendulum type come up in Automotive for some reason?
Also, I could never see how a 'damper' doesn't have a torsional stiffness. For it to dampen out motion it has to provide some relative movement and thus a stiffness between elements.

The largest issue with all of these (except pendulum) is the fact that they absorb the energy. And thus, if you are working with a system that for example needs to stay as synchronous as possible these are not ideal as they add compliance. On the other hand, if you can somehow provide a counteracting force/torque you don't need to add compliance.

RE: Harmonic dampers

Hi FeX32,

"..........I have not seen much of the pendulum type come up in Automotive for some reason?"

They are available, at least for a bunch of US engines.

They rattle audibly under some operating conditions.
A typical car enthusiast's xperience is along the lines of this -
" ... you can hear it loud and clear on startup and shut down only..... "
post 10 here -
http://www.corvetteforum.com/forums/c3-tech-perfor...

Gotta think not many car owners would enjoy that.


The manufacturer says this -
"Much like its namesake, the Rattler® will emit an audible warning that it's ready to strike down its enemy, torsional vibration."
http://news.compperformance.com/Instructions/Rattl...

Somewhat useless video.
http://www.summitracing.com/search/product-line/tc...

RE: Harmonic dampers

gruntguru, I also like the "true" damper, fluid dampers being the only kind I know of. They actually tend to prevent strong torsional oscillations and work for all frequencies. However, where oscillating mass absorbers null torsional displacement, twist, of the crank by taking on the movement themselves and do not actually damp out the oscillations, fluid dampers work by absorbing energy and can heat up. And, they only reduce oscillations depending on how much moveable mass they have and how viscous is their fluid.

RE: Harmonic dampers

(OP)
Thanks for the reading recommendations guys. I'll have to order some of these books.
In the meantime can anyone confirm that the pendulum dampers do need to be of a specific design to work on a specific order?
If it is specific to the order, are there other harmonics that would be of concern that it may not work on?

When I first started researching dampers the fluid dampers sounded like a great idea but as I started researching I started coming across a ton of people who had broken cranks while running them and entire car communities who swear it's worse than a solid pulley. Granted there was no science or engineering behind these claims and some could be non related. There were definitely a few though where skilled engine builders built several motors and kept getting crank or bottom end failure then stopped running the damper and stopped having bottom end problems.
If these things could possibly be related I would love to understand the science behind why. It has somewhat put me off of fluid dampers until I know more though.

I have also started to question elastomer dampers on heavily modified motors as it sounds like the damper will be tuned to a specific motor characteristic so if you add a lot of compression, displacement, boost, RPM or whatever then it seems quite possible it could no longer be suited for the motor.

An even bigger concern is the question of whether it is possible for the damper to amplify harmonics if the design is wrong for the motor?

RE: Harmonic dampers

I have also started to question elastomer dampers on heavily modified motors as it sounds like the damper will be tuned to a specific motor characteristic so if you add a lot of compression - No
displacement - yes if stroked
boost - No
RPM - Yes
An even bigger concern is the question of whether it is possible for the damper to amplify harmonics if the design is wrong for the motor? -Yes

But these are very basic questions. if you don't understand how a harmonic damper works then why are you expecting to stuff around with them successfully? If you aren't measuring TVs then how do you develop around them other than suck it and see?


Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Harmonic dampers

(OP)
That is the reason I started this thread.

I want to make a pulley that has an integrated trigger wheel. Most of my competitors make lightweight solid pulleys and for the 4AGE it seems to have minimal negative effect but that just means that it doesn't do damage that can be obviously attributed to the solid pulley. It doesn't tell us if a motor that went 60k miles with it might have gone 160k with the proper pulley.
So I could make a solid pulley and it would most likely be fine and my customers would happily buy them and run them.
On the other hand if I can develop something better that would be huge. Even if it wasn't the absolute best it could be if it was better than a solid pulley it would be a step in the right direction and a selling point.
This is why I was hoping there was at least one design that would dampen universally or would be able to work well enough with the proper formula. Or if not then if there were designs or formulas that could put me on the right track. I find this topic interesting enough that a little down the road I could see myself setting up a motor with a way to measure torsional distortion. That wouldn't be happening for a little while though.

Beyond that I was definitely looking for general information. Trying to get a better feel on how bad a solid pulley could be or if on the right motor if it could really be a non issue, but if it is then why would the OEM have wasted the time and development on it?
I recently found a company that will reman old OEM dampeners. But if the durometer or behavior of their elastomer is just a little different it could completely change the behavior of the pulley.

And then there are the aftermarket dampened pulleys.
These pulleys are designed for our motors.
http://www.bhjdynamics.com/index.php?main_page=ind...
They are supposed to be high performance pulleys but they don't have any qualifiers as far as what range they are designed for. I guess I should call them and see if they actually tested these designs on motors and see if they are intended for use with higher RPM or longer stroke motors.

It makes me wonder if these guys test all the motors they make pulleys for, or if they have their own internal formulas.
Same with the Rattler and this was the one I was really curious about. Do they test every motor they make a damper for? Or do they just use their formula?
If the latter what are the key points of that formula? The pendulum style seems like it should dampen any vibration because it will roll and absorb some energy of that vibration but people are saying it has to be tuned to the order to work properly. Is there any short easy answer to give an idea of why? Or is it a read the book to find out kind of answer?

RE: Harmonic dampers

The Hartog "Mechanical vibrations" book is among my faves right now, and has been for a few decades.
I own a bunch of those Dover reprinted tech books. Even Ignoring the tech content, Among the highest quality paper backs I've ever bought. My copy (over 25 years old) of DH's Mechanical Vibrations is quite worn, but not very yellowed, and the binding is solid.

Attached is a sample from the 1934 edition available on line.

RE: Harmonic dampers

"Trying to get a better feel on how bad a solid pulley could be or if on the right motor if it could really be a non issue, but if it is then why would the OEM have wasted the time and development on it? "


There is some middle ground. Not dangerous, but "nicer."
Original Studebaker V8. Image attached.

RE: Harmonic dampers

"Trying to get a better feel on how bad a solid pulley could be or if on the right motor if it could really be a non issue, but if it is then why would the OEM have wasted the time and development on it? "


There is some middle ground. Not dangerous, but "nicer."
Original Chevy V8 265 CID 1955.

As bore and stroke increased over the years up to 400 CID, and crank material and design changed, the "necessity" of a damper likely grew as well.

RE: Harmonic dampers

Tmoose,
I also have DH's text. It is good for sure.

Nestorides' text has the best engineering info on torsional dampers though. Some I never considered before were; viscous shear damper and slipping torque damper.

yoshimitsuspeed,
Each damper or absorber is designed for a particular engine. There can be considerable effort to design for a specific application.
There are cases when one is applicable to several engines. But this should be properly evaluated.
Maybe the viscus shear type or the simple tuned damped disc might be less sensitive.

A thought; In practice, has anyone come accross a pendulum damper fitted to the opposite end of the C/S to the flywheel? Like in the case on this side or just before the timing drive or accessory drive pulley?
It is illustrated in Nestorides' text like this but I cannot find an actual product in this location.

RE: Harmonic dampers

Hi FeX32,

" Some I never considered before were; viscous shear damper and slipping torque damper. "

Mercedes 300 SL "Gullwing" W198 used a friction crankshaft damper.
https://www.niemoeller.de/en/300SL/300SL/B040/3/c0...
Note the thick inertial disk that still pales compared to the large diameter fixed disk.

RE: Harmonic dampers

Hi Yoshimitsuspeed,

I am by no means an expert in pendulum dampers, but I have played with them enough to know someone who is. You may want to contact Bill Brogdon at bmepinc. In addition to many other things, Bill oversaw design of the direct drive high compression ratio 4 cylinder boxer that propelled the aircraft "Voyager" around the world in 1984. The relatively low speed high bmep high cylinder pressure direct drive nature of aircraft engines create a TV nightmare, and the highest bmep aircraft engines almost exclusively employ pendulum dampers.

I don't know if Bill can add much to what EHudson has already said, as Bill will also refer to Den Hartog regularly. If you choose to contact him, his website address is:

bmepinc.com

Regards,

Dick V.

RE: Harmonic dampers

Friction, viscous and (to a lesser extent) elastomeric dampers would all generate a lot of heat if the engine was continuously operated near a TV harmonic so it is not surprising that pendulum dampers would be favoured for aircraft engines.

je suis charlie

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