Dynamic force transmitted by hydraulic mount: Estimation in frequency domain using motion and/or pressure measurements and quasi-linear models

This article proposes indirect methods to estimate dynamic forces that are transmitted by a fixed or free decoupler type hydraulic engine mount to a rigid base. First, the linear system transfer functions that relate the force transmitted to the top chamber pressure and excitation displacement are derived in the Laplace and frequency domains; these clearly identify the roles of rubber and hydraulic force paths up to 50 Hz. Since hydraulic mounts are inherently nonlinear, a quasi-linear model is developed that incorporates amplitude-sensitive and spectrally-varying parameters such as top chamber compliance and rubber path properties (stiffness and damping). Alternate schemes based on a quasi-linear fluid system formulation work well as dynamic force spectra over a range of harmonic displacement excitations are successfully predicted given motion and/or pressure measurements; these compare well with measured forces over a range of frequencies and excitation amplitudes. In particular, the force to pressure transfer function model is quite promising. Conversely, the analogous mechanical system model fails as it yields highly inaccurate forces. The force time history is also briefly predicted by applying the Fourier expansion with an embedded quasi-linear fluid model with only the fundamental (excitation) frequency.