The dynamic behavior of pneumatic vibration isolators

Abstract

The ubiquity of pneumatic vibration isolators, especially in heavy road vehicle suspensions and in passenger rail vehicle secondary suspensions, has boosted research interest in these systems. Thermodynamic models have been used in order to inform and support engineering design decisions. Most models assume that the air inside the system undergoes a polytropic transformation during the compression/expansion cycle, but the necessary polytropic index value is often guessed at and seldom measured. This paper presents measured polytropic indexes that contradict the traditional assumptions with respect to its value. On a different note, the work presented in this paper also investigates the air flow through the restrictor (a component that is often used in suspension applications to introduce damping and adapt the frequency response function). The results show that this flow can be analyzed with utterly simple models.