[headers]

Originally Posted by vikram_d

That is a tuned mass damper and that is why it is so expensive. Trust me it is far from being a simple piece of molded rubber. I'm sure the weight of the rubber piece will be controlled within milligrams for it to function properly.

Adding to ^^: The vibrations are measured in 3d and the axis that has the max is first attended to.

Without the dampener - The harmonic vibrations will be transmitted to other parts of the chassis.

Manufacturing such pieces which are designed to work in a particular axis / frequency are no wonder expensive

Originally Posted by SPIKE ARRESTOR

Any idea about the shore hardness values required? Apart from vibrations (which is understood) what can happen if this part is not present?

Spike

I dont know the shore hardness values required - But I do know that without it - the NVH worsens.

The smoothness associated with the vehicle takes a negative as well as the sound Db ratings could be affected at say cruising speed at a particular engine rpm.

[vikram_d]

In this damper the shore hardness of the rubber will not be very important. It's shape and weight will be the most crucial factors.

Edit: On taking another look at the photo, I think the two downward extensions serve to bring the center of gravity of the damper lower.

[dhanushs]

Originally Posted by vikram_d

That is a tuned mass damper and that is why it is so expensive. Trust me it is far from being a simple piece of molded rubber. I'm sure the weight of the rubber piece will be controlled within milligrams for it to function properly.

I think vikram is right.

Originally Posted by khan_sultan

I wanted to know how it works/what it is for etc.

No. No plans. Just curious to what it is, what it does and HOW

I'm no expert, and haven't had a real life experience of handling this part.

But, by the looks of it, I think its a balancing mass, to balance out the unbalanced forces, produced due to the inertia forces associated with the rotating and reciprocating parts inside the transfer case.

A simple example is that, the centrifugal forces of a rotating shaft is balanced only if the center of the mass lies on the axis of rotation. If not, additional balancing masses are used to cancel out the unwanted forces causing vibrations etc..

[SPIKE ARRESTOR]

Originally Posted by khan_sultan

1. Why is this not present in say a Gypsy? Do MM Jeeps have this?

2. But don't you think PU will not absorb vibrations as much as rubber? I have seen PU body mounts and the vibrations/harshness through those are much more than rubber mounts

Khan_Sultan, has asked 2 VERY pertinent questions (see above). Why is this not present in all vehicles and why do PU mounts result in a change of vibration and harshness ? What differentiates between a PU body mount and one made of rubber?

Originally Posted by headers

Adding to ^^: The vibrations are measured in 3d and the axis that has the max is first attended to.

Did not understand the part above, could you explain?

Manufacturing such pieces which are designed to work in a particular axis / frequency are no wonder expensive

In this case, which axis is the component supposed to work?

I dont know the shore hardness values required - But I do know that without it - the NVH worsens.

I like that answer. NVH worsens with rubber polymer or PU ?

Originally Posted by vikram_d

In this damper the shore hardness of the rubber will not be very important. It's shape and weight will be the most crucial factors.

Are you sure on the shore hardness part? Shape and weight I agree, but the third part.. Any particular reason why you think so?

Consider the following case -

I need to do a vibration analysis of a wheel + tyre combo for ride optimization. I have a steel wheel + tyre combo which weighs X kg. I remove the steel wheel and replace it by an alloy wheel (less weight). The new combo now weighs Y kg, naturally X>Y. In order to compensate for the difference in weight (X-Y) w.r.t the original combo, I add weights on to the new combo to bring it closer to X.

Now, if we consider both these combinations as a vibrating system, does this new system have the same parameters as the old one i.e. stiffness, damping? Mass has been made same, so we can safely assume unsprung mass of the wheel combo remains the same. In other words, are the natural aka eigen frequencies the same? Take reasonable assumptions.

Seems like a vibrations class eh ?

Spike

PS- Why does the vibration level of a car change when running with overinflated / underinflated tires? Difference in air mass is understood, but what does it result in ?

[vikram_d]

Originally Posted by SPIKE ARRESTOR

Why is this not present in all vehicles and why do PU mounts result in a change of vibration and harshness ? What differentiates between a PU body mount and one made of rubber?

Why it is not present in all vehicles is a very generic question. The design of those vehicles and the parts of that vehicle may not need it.

PU results in change of vibration and harshness because it shore hardness is much higher than that of rubber.

Originally Posted by SPIKE ARRESTOR

Are you sure on the shore hardness part? Shape and weight I agree, but the third part.. Any particular reason why you think so?

Yes I am sure about the shore hardness bit in this particular case as there is not going to be any wear & tear on this part. The most that can happen to this part is that the rubber will harden with age and will lose it's damping properties. Since this is a mass damper, the weight of the component is more important than it's hardness.

Originally Posted by SPIKE ARRESTOR

I need to do a vibration analysis of a wheel + tyre combo for ride optimization. I have a steel wheel + tyre combo which weighs X kg. I remove the steel wheel and replace it by an alloy wheel (less weight). The new combo now weighs Y kg, naturally X>Y. In order to compensate for the difference in weight (X-Y) w.r.t the original combo, I add weights on to the new combo to bring it closer to X.

Now, if we consider both these combinations as a vibrating system, does this new system have the same parameters as the old one i.e. stiffness, damping? Mass has been made same, so we can safely assume unsprung mass of the wheel combo remains the same. In other words, are the natural aka eigen frequencies the same? Take reasonable assumptions.

No, the natural frequencies will not be the same as the material of both the wheels varies and they each have their own natural frequencies.

Originally Posted by SPIKE ARRESTOR

Seems like a vibrations class eh ?

Oh yes it does.

Originally Posted by SPIKE ARRESTOR

PS- Why does the vibration level of a car change when running with overinflated / underinflated tires? Difference in air mass is understood, but what does it result in ?

Simple answer really. This is because the excess/low pressure in the tyre is preventing the rubber from being it's natural bouncy/damping self.

With excess pressure the tyre cannot deform to soak up the vibrations. With low pressure the weight of the car is not allowing the tyre to spring back or come back to it's natural shape.

[Jaggu]

Arree just like wheel balancing uses weights, these are weights for gearbox / transfer case.

Why all vehicles dont have it? Maybe they dont vibrate so much thanks to lighter components etc or maybe they are not bothered with so much of refinement.

Why not PU? PU is hard, i will knock you with a cotton pillow OR a baseball bat. Which one would you prefer?

Sorry couldn't resist it, but exports please continue the serious talk

Khan very interesting observation though, now question to you. What makes you think that the various damper bushes that Gypsy GB/TC doesn't do the same thing this 400$ part does??

[khan_sultan]

Originally Posted by Jaggu

...What makes you think that the various damper bushes that Gypsy GB/TC doesn't do the same thing this 400$ part does??

I fully get the Gypsy TC Mounts helping in the damping part. They are wedged between two plates and hence damping with rubber mounts.

However, in this case, this is like a free hanging attachment to the TC. Just a metal clamp on one end of TC and this rubber mount at the end of the clamp. How does it damp?

I can now understand, somewhat, the weight/mass damping that this must be doing, but still don't fully understand it.

Next time, I take you under the vehicle & show it to you

[Jaggu]

Originally Posted by khan_sultan

I can now understand, somewhat, the weight/mass damping that this must be doing, but still don't fully understand it.

Next time, I take you under the vehicle & show it to you

Is it on the opp side to the prop shafts? Maybe this to break any harmonic vibration that might crop up at any particular rpm of the shaft? All for refinement at higher speeds.

Spikeeee reveal the secret will ya!

[vikram_d]

Originally Posted by khan_sultan

How does it damp?

I can now understand, somewhat, the weight/mass damping that this must be doing, but still don't fully understand it.

A video to explain it in simple terms. The two extensions at the bottom are doing exactly what is shown in the video.

http://m.youtube.com/watch?v=fuCdZLQOrAw

Edit: Hope this clears all doubts.

Edit 2: To see how much of a difference the damper is making you can remove it and take a short test drive.

[vikram_d]

The simplest form of mass damper that is found on all vehicles with exhaust systems and I'm pretty that we have all seen this part at some point or another.



It may not be perfectly tuned but it does an excellent job.

[Samurai]

Originally Posted by vikram_d

The simplest form of mass damper that is found on all vehicles with exhaust systems and I'm pretty that we have all seen this part at some point or another.

This is the one with Grand Vitara.

[vikram_d]

Originally Posted by Samurai

This is the one with Grand Vitara.

Attachment 1062222

Shapes may vary, but it's a damper nonetheless and it does exactly what has been shown in the video.

[headers]

The Marutis and the Mahindras too have engine / body mounts similar to that explained above - A close inspection of the under body of a vehicle will reveal it.

Infact, modern diesel engine's engine mount play a HUGE role in arresting the vibrations of the engine in an automobile.

This is apart from the balancers in the system.

[SPIKE ARRESTOR]

Originally Posted by Jaggu

Maybe this to break any harmonic vibration that might crop up at any particular rpm of the shaft? All for refinement at higher speeds.

Spikeeee reveal the secret will ya!

Yes you are right, this is to prevent component damage due to resonance. The video shown above explains how this works but what actually happens with the arrangement is not clearly explained.

The video is good though, and I hope it answers the raised questions.

However, there are a few corrections -

1. A mass alone cannot cause any desired damping. Any object that occupies mass has stiffness and in some cases damping too. So be it a pen, pencil, eraser or ... rubber, everything has a mass and a specified stiffness. It is the combination of the spring + mass + damper which does the trick and not the mass alone. If mass alone was so important, why choose only a rubber polymer then? So, there is no "Mass damper" as such. Mass can act as a balancer (e.g. crankshafts), but mass alone cannot dampen, material properties come into play.
In other words, shore hardness is important.

2. The pictures shown above (of exhaust hangers) are functionally different from the question raised by Khan_Sultan. Remove the exhaust hangers and tie the exhaust with a rope, there won't be any difference. Try doing that with the other part at higher speeds, results could be nasty.

3. It is advisable not to drive without the dynamic damper, specially at high speeds. If still going ahead, carry some Mseal and transfer case oil along. There are good chances that these will come in handy.

Spike

[DirtyDan]

Originally Posted by headers

Infact, modern diesel engine's engine mount play a HUGE role in arresting the vibrations of the engine in an automobile.

This is apart from the balancers in the system.

Starting about 25 years ago the auto industry began pushing diesels as a partial answer to the petroleum energy crisis (rightly or wrongly). They had to overcome diesel's poor public image of stinky, loud, shaking contraptions. Damping, CRD, new turbo technology, advanced ECU programs/ignition programs, all came out of that.

Interesting that engineers would opt for expensive damping when adding a few bolts would SEEM to be the common sense solution.