Estimation of the damping coefficient of a suspenion

  • Automotive
  • Thread starter serbring
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  • #1
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Main Question or Discussion Point

Hi all,

I have a suspended seat with a scissor mechanism like the following:
fb2c50db-5ac3-416f-a643-3c32f76c4924.jpg



This seat is composed of coil spring and a hydraulic damper. My aim is to develop a multibody model of that seat. Actually, my model is quite complete, only the parameters of damper are missing (i.e. the damping coefficient with respect to its piston speed). I do not have any technical details about it, so I need to estimate it. I am thinking to use a system identification approach, that means, applying a known excitation to the seat, measure the displacement of the seat cushion and tune the model parameter so that the measured displacement will be reproduced. I do not have any rig so that I can easily apply a known excitation. I was thinking to excite the seat by applying an impulse (falling mass at a certain height) to the seat cushion. What do you think about this approach? Do you know an easier approach to get the damping curve of the damper?

Thanks,

best regards
 

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  • #2
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The damper manufacturer must supply that information. Otherwise, no seat manufacturer would know which size damper to buy.
 
  • #3
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Hi Anorlunda,

you are on right, unfortunately I do not work for any seat manufacturer. I have contacted both the seat and the damper manufacturer and both have not supplied any information. So I was thinking to use an experimental mode.

PS
I am sorry for the late reply, I trusted on the email alert :|
 
  • #4
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If you know the spring constant, you can estimate the damper coefficient by displacing the seat, releasing it, and then measuring the subsequent displacement vs time.
 
  • #5
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Yep! you're on right. Easy and safe. This made me think, that this type of dampers has two different coefficients, one in compression and the other in rebound, right?
 
  • #6
19,916
4,093
Yep! you're on right. Easy and safe. This made me think, that this type of dampers has two different coefficients, one in compression and the other in rebound, right?
I don't know about that. Damping coefficients are usually assumed to be the same for both directions.
 
  • #7
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  • #8
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How about you just experiment. 60 seconds of searchiing found this item, an adustable force air damper.
https://www.alibaba.com/product-detail/Hydraulic-dampers-compression-uk-adjustable-force_60742082092.html?spm=a2700.7724838.2017115.49.57c31d936fIF7q

They are inexpensive. How about just buying one, then use the adjustment to tune it to your needs?
Which kind of test you are thinking about? I need to find the parameters of the damper that is already installed in a seat suspension
 
  • #9
8,239
5,051
Which kind of test you are thinking about? I need to find the parameters of the damper that is already installed in a seat suspension
Ah, I see. Are you able to make a deflection, then release it while accurately measuring the position versus time recovery? That is similar to excitation that you suggested in #1, except that instead of a periodic excitation it would be a step function. Success depends on the instrumentation available.

Come to think of it, a video recording analyzed frame-by-frame would be a good way to measure deflection versus time.

Edit: The whole test and analysis might be easier if you removed the damper from the chair.
 
Last edited:
  • #10
cjl
Science Advisor
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Yep! you're on right. Easy and safe. This made me think, that this type of dampers has two different coefficients, one in compression and the other in rebound, right?
I don't know about shocks for seats, but the shocks used for high end sports car suspensions frequently have 3 separate characteristics - high speed compression, low speed compression, and rebound. The simple model used in physics problems frequently assumes that there's a single damping coefficient, but this is frequently not the case in reality.
 
  • #11
269
2
Ah, I see. Are you able to make a deflection, then release it while accurately measuring the position versus time recovery? That is similar to excitation that you suggested in #1, except that instead of a periodic excitation it would be a step function. Success depends on the instrumentation available.

Come to think of it, a video recording analyzed frame-by-frame would be a good way to measure deflection versus time.

Edit: The whole test and analysis might be easier if you removed the damper from the chair.
I know that the best is testing only the damper, but I do not have any tool to apply a known load. Any suggestion is appreciated. My idea is to install very precise draw-wire displacement sensors. I do also have a high speed camera.
 

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