Advanced Hydraulically Damped Elastomeric Component Models

This paper describes methods for modeling and characterization of hydraulically damped elastomeric mounts. The objective of the work is to be able to fit models to existing parts, describe modifications to current components and to correctly model and specify hydromounts in virtual prototype vehicles. The model used is physically based and begins with the modeling of the basic mechanical properties of the elastomeric element of the mount. It is shown that it is vital to consider the nonlinear physics of the fluid channel, particularly in relation to the hydromechanical characteristics of the elastomeric element. It is shown that the key to the hydraulic damping phenomenon is the internal resonance of the hydraulic fluid in the damping channel on the volumetric stiffness of the fluid cavity in the elastomer. Furthermore, the importance of orifice losses during the pumping of the hydraulic fluid through the channel is shown. The model has been developed in-house using commercial spreadsheet software and has also been implemented as a FORTRAN-based differential equation model in MSC-ADAMS™ multibody simulation software. Hydraulically damped mounts often include a decoupling device such as a mechanically constrained diaphragm, which can reduce noise transmission for small inputs: it is shown how such devices can be modeled and the concomitant vibration control compromise is considered. The paper emphasizes the importance of using a minimal set of physical parameters to describe the mechanical behavior of the mount and also considers the inverse problem of fitting the parameters to industry standard tests and measurements.