Harmonic dampers 5

[yoshimitsuspeed]

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-rattler-balancer-tech-review/

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?

 

[FeX32]

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,

 

[GregLocock]

http://www.abebooks.co.uk/book-search/title/torsional-vibration/author/wilson/

Cheers

Greg Locock


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[EHudson]

"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.

 

[FeX32]

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" ?

 

[Tmoose]

The search function at SAE.org got over 12,000 hits for "torsional damper."
Please see attached image


I think civilians can preview the first 4 or 5 pages right on the webpage.
Here is the page for the 1949 paper by Caterpillar.

http://papers.sae.org/490032/

click on the "view" window over to the right.

 

[FeX32]

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

 

[GregLocock]

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


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[gruntguru]

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

 

[GregLocock]

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


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[FeX32]

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.

 

[Tmoose]

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...rmonic-damper-anyone-try-the-tci-rattler.html

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/Rattler.pdf

Somewhat useless video.

http://www.summitracing.com/search/product-line/tci-rattler-torsional-vibration-absorbers

 

[140Airpower]

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.

 

[yoshimitsuspeed]

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?

 

[GregLocock]

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


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[yoshimitsuspeed]

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=index&cPath=9

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?

 

[Tmoose]

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.

 

[Tmoose]

"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.

 

[Tmoose]

"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.

 

[FeX32]

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.

 

[Tmoose]

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/c03141-schleifscheibe-f-schwingungsdaempf

Note the thick inertial disk that still pales compared to the large diameter fixed disk.