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How to calculate the correct trim load to put in airspring setting?

Hello,

I have a rigid axle model with airsprings on it. Running the analyses I have to set the airspring into "Trim Load" rather than "Auto Trim Load". However, when I am trying different trim loads, I get totally differnt results for suspension characteristics, such as Roll Center Height, Torsional Stiffness etc.

When I set the axle to be rigid the variation is much lower while in a flexible axle the results are different in a wider range.

According to the calculation process for Auto Trim Load and Trim Load I can rationalise those changes in the results but now the question is how can one calculate a reasonable value to put in for the Trim Load setting?

I've attached a picture of sample runs which I did for rigid and flexible axle including different trim loads as well as Auto Trim Load.

Thanks in advance for sharing your experience and knowledge.

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0 Jesper Slattengren over 8 years ago

Use the values calculated by the Auto Trim Load and put that in for Trim Load.

When you change trim load, you get different ride height, which could change the roll center slightly. But for a rigid axle it should not change that much.

Your plot indicates that your flexible axle is way too soft. Roll center height is directly linked to camber change, so this indicates that you have a lot of camber flex in your axle, most likely local deformation close to the wheel.
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0 MMD over 8 years ago

You are indeed correct. I have too much change in my camber with a flexible body as well as in my RC height. Do you mean the airspring force (nsl_..., force) when I run with Auto Trim Load?
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0 Jesper Slattengren over 8 years ago

Yes, take the fist value of that result (after the static). That should be the preload calculated by the automatic routine.
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