# Air Spring

Sealed translational air spring

**Library:**Simscape / Driveline / Couplings & Drives

## Description

The Air Spring block represents a generic sealed translational pneumatic spring that isolates equipment from shocks and vibrations. The compressibility of gas gives air springs desirable isolation performance. Air springs are common in automotive and industrial applications where low spring rate and low natural frequency are beneficial. Air springs can help you to:

Reduce wear and tear on the sprung mass.

Reduce the wear and tear that the unsprung mass deals to infrastructure.

Lighten suspension systems to allow for greater total mass.

Filter out specific unwanted frequencies.

Air springs consist of bellows that confine a column of compressed air or other gas. The air bears the force of the load, and the bellows hold the air. Sealed air springs maintain a constant mass of air, so the increasing load lowers the volume of air and the resulting spring rate. The reverse is also true. The natural frequency of a sealed air spring system also depends on this relationship. Due to the large amount of variability in air spring requirements and performance, manufacturers commonly provide pressure characteristic tables for each model.

Based on the data that you possess, you can set **Parameterization** to
`Load as a function of height`

or ```
Stiffness as
a function of height
```

. The Air Spring
block uses the information that you enter to create a lookup table. The lookup table
allows the block to simulate the nonlinear force response of an arbitrary air spring.
This is the effective force to achieve a given height, which is equivalent to the
**Load vector** parameter or the element-wise product of the
**Stiffness vector** parameter and the **Height
vector** parameter. For more information about using lookup tables in
Simscape™, see `tablelookup`

.

The block takes the relative translational motion between port **R** and
port **C** to evaluate the air spring height and velocity and uses this
information to find the appropriate lookup table entry. The block computes the nonlinear
effective force response *ΣF(x(t),t)*, such that:

$$\sum F(x(t),t)}=-c(x(t))\dot{x}(t)-k(x(t))x(t)+{F}_{external},$$

where

*x(t)*is the height of the spring relative to the undisturbed position.*ẋ(t)*is the velocity of the spring.*-c(x(t))ẋ(t)*is the viscous damping force. The damping coefficient*c*varies with spring height.*-k(x(t))x(t)*is the stiffness force. The spring coefficient*k*varies with spring height.*F*is the force transmitted through the ports._{external}

You can choose whether to implement hard stops in your model on the **Hard
Stops** tab. When you set **Hard stop at full extension**
or **Hard stop at full compression** to `On`

,
you can specify a boundary height, the stiffness and damping at that height, and the
length of the transition region. The hard stops are equivalent to the Translational Hard Stop block.

### Variables

Use the **Variables** tab to set the priority and initial target
values for the block variables before simulating. For more information, see Set Priority and Initial Target for Block Variables.

The sign of the **Force** variable is negative when the load is
positive.

## Ports

### Conserving

## Parameters

## Version History

**Introduced in R2021a**