We start that process by asking six questions:

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1. Is the component stationary or mobile?

Stationary and mobile components take two very different approaches. Stationary components require a simple mounting system where you sandwich a vibration isolating material between two metal pieces. This simple solution can offer more accurate machining, longer product life, and reduced maintenance and is cost-effective.

Mobile devices require more specific and often complex solutions to make sure they are safe. Mobile equipment, particularly off-highway vehicles and marine applications, for example, experience more vibration than their stationary counterparts. Now, what if that rubber were to fail? Would your unit remain intact or separate from your system? Selecting a mount that is “safetied” becomes a critical consideration. You also need to factor in the varied external conditions they will experience. Numerous mounts can accommodate these, but they will need to be carefully selected to meet user-specific criteria perfectly.

2. What is the weight of the component we are isolating?

The weight of the component will directly impact what materials can be used to isolate them. While some materials may work well with your vibration. Static and dynamic loading on the isolation system need to be considered. Coupled with the inertial forces can the isolators contend with this? Pound-force per square inch (PSI) is a common failure point for incorrect materials.

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3. How many mounting points will you have?

The mounting points are important and related both to weight and motion. The weight of the piece compared to the number of mounting points inform the minimum material strength. The number of mounting points can also lead to substantial differences in design.

4. Center of gravity details

For an effective vibration isolator, we must know where the center of gravity is. We also need to know where it is in relation to our isolators. We need this to get an accurate picture of the system dynamics, it becomes a very important isolator design consideration Again, this information is tied to understanding the loads and potential loads at the mounting points. Offset centers of gravity can cause very different loads for individual isolators.

5. What is the vibration source we are isolating?

Fans, motors, and pumps require different approaches to vibration isolation. Because each has variable frequencies and maximum allowable motion, each will require specific types of materials and mounting systems.

6. What are the environmental conditions?

Different elastomers have different responses to the environments in which they operate.. All of these questions are vital to know which materials will respond best for your application.

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Tuned Vibration Dampers- Optimal parameters and general discussion

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Tuned Vibration Dampers- Optimal parameters and general discussion

Tuned Vibration Dampers- Optimal parameters and general discussion

FeX32

(Mechanical)

(OP)

24 Jan 18 03:57

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 (

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

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 saysThis 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

GregLocock

(Automotive)

24 Jan 18 10:38

ie it all depends on what you mean.

Imagine a simple 2dof system. If the masses are very roughly equal then the attenuation at the initial resonance is excellent, and does not rely on damping. Away from that speed, yes damping is important.ie it all depends on what you mean.

Cheers

Greg Locock


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RE: Tuned Vibration Dampers- Optimal parameters and general discussion

FeX32

(Mechanical)

(OP)

24 Jan 18 23:44
Ceramic Insulators vs. Porcelain Insulators: Which is Best?

Thanks Greg. I know what you mean - basically I am trying to understand more about what detail to look for in TVD development and how important damping is - from an overall performance perspective.
Is there a key analysis you would typically conduct?

RE: Tuned Vibration Dampers- Optimal parameters and general discussion

GregLocock

(Automotive)

25 Jan 18 00:07

To be honest I just order a selection of geometries and rubbers the supplier recommends for the given crankshaft modes we don't like (bending and torsion), and then either measure TVs or select them by ear. I don't remember actually measuring anything for bending but I suppose crank block acceleration would do. Bending I usually tune by ear.

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

FeX32

(Mechanical)

(OP)

25 Jan 18 00:39

Thank you Greg.
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

GregLocock

(Automotive)

25 Jan 18 04:53

"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.

"When tuning by ear - do you think this could also be done by noise analysis?" You should see a change in noise or vibration at the bending frequency. Normally i'm a fan of objective analysis but in the case of crankshaft bending modes the right tune stands out."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


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RE: Tuned Vibration Dampers- Optimal parameters and general discussion

FeX32

(Mechanical)

(OP)

25 Jan 18 23:16

Thanks Greg.
"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

GregLocock

(Automotive)

26 Jan 18 01:30

The bending mode is not an objective problem (usually), it just causes poor sound quality. Not every car gets a bending absorber, I'd be a little surprised if most cars did not have a TV damper. You can get away without one in some cases, but they are there for crankshaft fatigue primarily, as well as noise quality. I think 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?

Cheers

Greg Locock


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RE: Tuned Vibration Dampers- Optimal parameters and general discussion

FeX32

(Mechanical)

(OP)

26 Jan 18 03:36

Thank you again.
"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

GregLocock

(Automotive)

26 Jan 18 07:23

I don't do NVH any more, I don't know what they use.

In the eighties we used a separate little harmonic damper for bending. It bolted onto the crank nose inside the pulley. However in the nineties Ford Australia started using a design of TV damper in which the rubber was profiled in side view, which meant that for a given TV tune you could vary the bending tune. Very clever.I don't do NVH any more, I don't know what they use.

Cheers

Greg Locock


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RE: Tuned Vibration Dampers- Optimal parameters and general discussion

GregLocock

(Automotive)

26 Jan 18 08:00

I've just employed a poorly trained CAD guy to draw a TV damper. Changing the nominated radius to infinity or even negative alters the bending frequency of the damper while having little effect on the torsional frequency.

Cheers

Greg Locock


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RE: Tuned Vibration Dampers- Optimal parameters and general discussion

FeX32

(Mechanical)

(OP)

27 Jan 18 16:21

That's some great info Greg. Thanks again.

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

GregLocock

(Automotive)

27 Jan 18 21:34

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


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I'd guess we were around 60-80 Shore A, whatever damping that gives. I wouldn't worry about the bending mode, nobody used to. On an I6 it is audible, but not an I4, generally. On the LT5 Corvette engine, which had a crank nose mounted gear type oil pump, the bending mode was strong enough to smash the pump up, so that got a bending damper.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.CheersGreg LocockNew here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies

RE: Tuned Vibration Dampers- Optimal parameters and general discussion

FeX32

(Mechanical)

(OP)

28 Jan 18 16:33

Thanks Greg.

"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

GregLocock

(Automotive)

28 Jan 18 20:32

I've never sat down and worked it out, but if you have a lot of damping the damper mass can't move as much so it can't absorb as much energy in the rubber, is a handwavy explanation. A few minutes in excel would prove it one way or the other. Viscous dampers are a whole separate thing, although I suspect the same applies in some respects. I haven't tuned one.

Cheers

Greg Locock


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RE: Tuned Vibration Dampers- Optimal parameters and general discussion

FeX32

(Mechanical)

(OP)

29 Jan 18 03:43

hmm. Thanks again Greg.
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.

RE: Tuned Vibration Dampers- Optimal parameters and general discussion

FeX32

(Mechanical)

(OP)

9 Apr 18 23:04

Hi Greg,

Another question comes to mind when looking at TVDs.

If I put a certain amount of energy (from combustion) into the crankshaft and it vibrates torsionally at a certain speed there will be a certain energy associated with this vibration. If we now put a TVD (not has less vibration at this speed), does the total energy change in the system? That is, does reducing the vibration translate to a fuel efficiency gain?

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