Dynamic characterization of air spring for AVC applications

Many engineering applications requires for the use of resilient mounts whose main scope is to decouple the vibration flow from the source to the receiving structure. In most of the cases, the provided design characteristics of these components are limited to the static stiffness and no information on the their dynamic behavior is provided. This represents a drawback while optimizing the resilient mounting of large vibrating machinery where every knowledge of the dynamics of the vibration paths plays an important role. In the years, to improve isolation performance of the mounts, air springs, instead of the full rubber mounts, have been adopted. These consists of a rubber sleeve, with appropriate endings, filled up with air at the appropriate pressure. Again the manufacturers do not provide much of the information, the engineers would need to use those devices at their best. In this work the authors describe the testing machine that has been builded at the LVA to derive the force vs frequency vs pressure plots of a set of commercial air spring. The machine can measure the forces both above and below the device, allowing to determine, directly, in three directions, the transmissibility as function of the frequency and of the applied pressure. The preload acting on the spring, as well as the internal pressure, can also be modified allowing for a more accurate system description. The characteristics curves derived for the air-spring in such a way, will be used within a simple SDOF AVC system. The performances of this solution will be compared with the performance of an analogous system using only the commonly available static deflection value. The work clearly exhibits the importance of the accurate measure of the dynamics properties of the mounts, and the relatively simple set-up with which these data can be acquired.