Suspension travel value not matching with calculated value
Hello,
I've built a 3 wheeler model on MotionView to analyze its handling during various standard tests. During Sinusoidal steering test, the Suspension travel was plotted against time and this plot shows a non-zero spring deflection at 0 seconds. Moreover, when the spring deflection is calculated manually using the spring stiffness and the tire load, the value does not match with the deflection value given in the plot. Kindly let me know why this is happening and how i could set the initial deflection at 0 seconds to 0mm.
Thank you
Answers
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Hello Vinayanand - Have you first validated your model at the axle level? The spring preload needs to be set correctly in order to maintain ride height, for a given corner weight (i.e. tire normal load) - this requires a few iterations with simulation end time set to a small value, say 0.5 seconds.
BTW, your hand calculation is correct only if the spring to wheel travel ratio is 1:1, which it rarely is in a real vehicle. If you haven't, please read up on motion or installation ratio.
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Thank you for the response, sir. The motion ratio is 1 and the spring is mounted vertically. I would also like to mention that the suspension travel plot of sinusoidal steering test in the default full vehicle model doesn't start from 0 at 0 seconds either.
Could you please let me know how I can ensure that the preload values on the springs are correct?
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Spring preload is set by monitoring the normal load on the tire, if you cannot do it at the axle level with a half-car model (or in your case, a 1/3rd car model
) . There are two ways to set preload, see screenshot below. One is directly by setting the preload value, the other is by setting the free length of the spring. The latter is possible only if you have design data for the spring. Use the formula, normal load x motion ratio squared as an approximation, then iterate the preload value until you get the correct ride height, or normal load on the tire.
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Altair Employee