Tuned Vibration Dampers- Optimal parameters and general discussion
Tuned Vibration Dampers- Optimal parameters and general discussion
(OP)
Gents,
I have a general question for the experts here that have tuned or designed engine/crankshaft tuned vibration dampers before. (preferably the kind on the C/S nose)
I have been reading through some of the info on the forum here in this regard and am wondering if someone has some good insight about a comment in this old thread (http://www.eng-tips.com/viewthread.cfm?qid=260497).
In it about halfway down ivymike says
This comment about the TVD that were the most effective being the ones that didn't necessarily dissipate the most energy is counter-intuitive to an extent. I have done a decent amount of theoretical linear TVD work before and can know from that there is an optimal damping that reduces the effectiveness at the frequency of interest but broadens its working range so that it doesn't create 2 ineffective regions below and above this frequency of interest.
Maybe he is really just referring to the damping and not energy - is it possible to look at this from strictly an energy point of view?
Any comments are appreciated.
Thank you.
Fe
I have a general question for the experts here that have tuned or designed engine/crankshaft tuned vibration dampers before. (preferably the kind on the C/S nose)
I have been reading through some of the info on the forum here in this regard and am wondering if someone has some good insight about a comment in this old thread (http://www.eng-tips.com/viewthread.cfm?qid=260497).
In it about halfway down ivymike says
Quote (ivymike)
"I quit reading it after the author claimed that his dampener both absorbed less power and also provided greater dampening. I don't believe the two results are mutually compatible; greater dampening would also imply greater energy absorption.
"
seven years ago when I last did TV analysis on a regular basis, that result was not uncommon. The most effective damper commonly did not dissipate the most heat - they often dissipated less heat than those which were less effective at reducing vibrations. It's a bit fuzzy now, but I think that result was common with elastomeric or viscoelastic dampers, and not so much with viscous ones.
This comment about the TVD that were the most effective being the ones that didn't necessarily dissipate the most energy is counter-intuitive to an extent. I have done a decent amount of theoretical linear TVD work before and can know from that there is an optimal damping that reduces the effectiveness at the frequency of interest but broadens its working range so that it doesn't create 2 ineffective regions below and above this frequency of interest.
Maybe he is really just referring to the damping and not energy - is it possible to look at this from strictly an energy point of view?
Any comments are appreciated.
Thank you.
Fe





RE: Tuned Vibration Dampers- Optimal parameters and general discussion
ie it all depends on what you mean.
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: Tuned Vibration Dampers- Optimal parameters and general discussion
Is there a key analysis you would typically conduct?
RE: Tuned Vibration Dampers- Optimal parameters and general discussion
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: Tuned Vibration Dampers- Optimal parameters and general discussion
I didn't realize that these rubber TVD's are also utilized for the bending mode as well. When tuning by ear - do you think this could also be done by noise analysis?
Also, I assume you are testing on engine dyno?
And do you think there is a method to verify performance without having an engine to test on?
Like if you were targeting a certain mode and frequency you could test the TVD separately from the engine to correlate potential performance?
Thanks again.
RE: Tuned Vibration Dampers- Optimal parameters and general discussion
"Also, I assume you are testing on engine dyno?" No,in car usually.
"And do you think there is a method to verify performance without having an engine to test on? Like if you were targeting a certain mode and frequency you could test the TVD separately from the engine to correlate potential performance? "
In the more general case of tuning tuned absorbers we found that hammer testing the absorber bolted to a large lump of concrete was a remarkably poor indicator of its performance in the car.
I don't know why.
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: Tuned Vibration Dampers- Optimal parameters and general discussion
"In the more general case of tuning tuned absorbers we found that hammer testing the absorber bolted to a large lump of concrete was a remarkably poor indicator of its performance in the car."
What if you excite the TVD torsionally and measure response to correlate with damping - would this be a way to correlate?
And how important is the bending mode in these? Does the supplier tune to this mode? Are the frequencies close to the torsional mode?
RE: Tuned Vibration Dampers- Optimal parameters and general discussion
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: Tuned Vibration Dampers- Optimal parameters and general discussion
"Not every car gets a bending absorber,"
So are there absorbers available that are only for this mode, or are torsional dampers tuned to both?
"your proposed torsional test is the best hope for a rig test, but if you are going to all that trouble why not just stick it on the engine?"
I understand what you mean here; but if you don't have the engine to test with (say it's not built yet) then there must be a method to propose an optimal TVD - while only having a simulation with proposed crank geometry.
What do you guys usually use for simulations of this nature?
RE: Tuned Vibration Dampers- Optimal parameters and general discussion
I don't do NVH any more, I don't know what they use.
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: Tuned Vibration Dampers- Optimal parameters and general discussion
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: Tuned Vibration Dampers- Optimal parameters and general discussion
That is a clever idea using the curvature to effect the bending mode.
So I can conclude that if we tune the torsional mode out without considering the bending mode it can be a bad thing?
I would assume so.
Do you remember what kind of damping factors you were using? I assume the damping of these devices are just as if not more important than adjusting the natural frequency. Is this generally correct?
RE: Tuned Vibration Dampers- Optimal parameters and general discussion
Yes tuning for frequency is much more important than the damping. In the more general case of tuned absorbers too much damping is often a bad thing.
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: Tuned Vibration Dampers- Optimal parameters and general discussion
"In the more general case of tuned absorbers too much damping is often a bad thing."
Can you elaborate? If there is lots of damping it guarantees that the TVD doesn't create another 2 resonance conditions that have high amplitude as well.
What about viscous dampers? They are not tuned for frequency but have high damping across the board?
RE: Tuned Vibration Dampers- Optimal parameters and general discussion
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: Tuned Vibration Dampers- Optimal parameters and general discussion
The viscous dampers seem to just add damping across the board and are maybe only on engines that are highly dynamic. Not sure how true this is nowadays.