4-post test rig for damper setup 2

[nadica]

Dear All,

I am looking for information about the use of the 4-post test rig for damper setup evaluation. If anyone would be kind to share his/her knowledge or would point me to the source of information, I would like to know what excitation is used and what measures are evaluated to compare two damper settings for grip. Is transient response evaluation a part of the process or it is usually focused on grip level?

Many thanks in advance,

Zoltan

 

[lateapex]

There's some good info here:

http://insideracingtechnology.com/o7postshkr.htm

 

[cibachrome]

You said 4 post. Racing usually requires 3 more for body reaction control, including aero effects, that's why 7 post posting is posted. If all you have is 4, you could do some intersting rail shipping testing, not much value for race prep. You'll need some track measurements for 7 posting: body accelerations ---> position. Then you can do contact patch footprint optimization. Debate is all about rolling vs non-rolling tire and no combined sideforce. Once you have these neural transformations, the car will be fast. A driver may not want to drive the setup you arrive at, though. Good example is coil binding. SAE paper on this subject a few years back.

 

[PTwizz]

There is a great deal to be gained from 4 post testing without any body actuation. Inputs would usually cover heave, pitch and warp modes, each using a sweep of frequencies from 0.5Hz to 30Hz. This can also be done with some simulated downforce (using air actuators with minimal damping and momentum).
Probably most useful among the results from such testing will be contact patch load variation (i.e. grip).
There will also be a number or derived results, including installation stiffness.
As mentioned above, rig testing shows what's good for the car. Drivers normally require some changes to a rig set up.

Pete.

 

[gt6racer2]

Pete is right on. You can analyse the vehicle response to inputs, but the correlation to optimized rig Vs reality is often difficult in race context.
The tire force variation is a key measure.

 

[nadica]

Dear All,
Thank you for your posts!
I found the article about the Ohlins rig quite interesting. My main interest is rally and touring cars so I am not sure how dominant the pitch issue is.

Pete and gt6racer2,
Both of you mentioned load variation. The article suggested by lateapex shows 'grip disturbance' charts and that suggest me to work with the gradient of the force vs time curve. Any thought on that?

Many Thanks,
Zoltan

 

[PTwizz]

I suspect 'grip disturbance' is probably the same as, or a direct function of, contact patch load variation.
I assume the force/time curve is force measured at the contact patch. The object would be to keep this curve smooth, with rates of force change kept to a minimum.

This approach will lead (broadly) to soft springing and linear damping, both good for grip, but less so for driver feel and aero/ride height control.

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