Defining Force data against varying pressure values for an AirSpring


A frequent question that has been asked about AirSprings in MotionView. How is the force based off a pressure determined? 

By looking over the .asg file (attached). The first column in the XY_DATA table contains spring heights at which measured or calculated forces are quoted in the second through last columns. In the example below, there are 6 columns - the first one is spring height. Each of the second through sixth columns correspond to force values at each of the pressures in the Z_DATA list, for each spring height. 

A screenshot of a graphDescription automatically generated

The trim load corresponds to preload in a normal spring-damper entity, which should be calibrated to the observed corner weight minus unsprung mass.

Trim height is installed height of the spring at the "as-modeled" ride height of the suspension.

Together, these establish the baseline pressure - the table is then interpolated to find the corresponding force of the spring to maintain its height.

The PARAMETERS block is fed to an underlying geometric model.

A diagram of height and heightDescription automatically generated

Attached is an example model of the AirSpring with a displacement input to compress the spring by 15 mm.

Important Note:  the air spring is only able to represent a rolling lobe airspring, the volume/pressure calculations will not be accurate enough for a convolute type spring, but we have a different solution for that. The simplest approach is a non-linear spring-damper but this only works for a single loading condition.