Dynamic evaluation of hydraulic elastomeric mounts

M.Phil.This study identifies and evaluates dynamic models used to characterise the dynamic stiffness and phase angle of hydraulic elastomeric mounts that are primarily used as engine and operator cab isolators in vehicular applications. Linear models developed for hydraulic elastomeric mounts are analysed for their suitability to be used to characterise the dynamic stiffness and its phase angle in the low and high frequency range. A sensitivity analysis provides insight into the parameters with a high level of sensitivity to changes in model parameters. The models selected from the linear analysis are enhanced and updated by performing a quasi-linear analysis to compensate for the dynamic behaviour of certain parameters. Non-linear dynamic behaviour of the decoupler is also investigated. These models are then verified experimentally. To set-up an analytical model that can be used to predict the dynamic characteristics of the hydraulic elastomeric mount it is necessary to develop a physical model from which the system differential equations are extracted. From the physical model flow continuity equations and fluid momentum equations are developed to obtain an expression that describe the fluid response in the inertia track and decoupler respectively. Lumped parameter mechanical models are developed next from which equivalent differential equations are derived to describe the internal dynamics of the hydraulic mount. These differential equations along with the transmitted force equation directly derived from the physical model are used to develop the dynamic stiffness transfer function. Time domain input displacement and output transmitted force data are taken at a specific frequency and amplitude, and are used to generate hysteresis loops to extract the dynamic stiffness and phase angles. For most of the computational effort, both analytical and experimental, MATLAB programs are written to perform curve fitting, FFT calculation, numerical integration and dynamical simulation. Emphasis is placed on the dynamic considerations of hydraulic mount design in the automotive industry and where machines are subjected to shock and vibration. The results and techniques used to model and the mounts are useful to designers in the field of shock and vibration isolation. Finally, the aim of the work is to keep the dynamic models as simple as possible, to be used effectively in the identification of the structural dynamic characteristics of hydraulic elastomeric mounts. To avoid complexity two models are used to describe the dynamics of the mount, one model for the low frequency, large amplitude conditions and one for the high frequency, small amplitude conditions. The information is then used to determine how the mount will respond under certain dynamical conditions