A new approach for double-notch frequency hydraulic mounts

Passive hydraulic engine mounts are broadly applied to the aerospace applications to isolate the cabin from the engine noise and vibration. In aerospace applications involving turbofan engines, the notch frequency of each hydraulic engine mount is adjusted to either engine low speed shaft imbalance excitation frequency (N1) or to engine high speed shaft imbalance excitation frequency (N2) at the cruise condition. Since most of today's passive hydraulic engine mount designs have only one notch, isolation is only possible at N1 or at N2, but not at both. In this paper, a novel double-notch passive hydraulic engine mount design is described, which has two notch frequencies, and therefore can provide vibration and noise isolation at two distinct frequencies. Also in this new design, one can use two working fluids, one being a controllable fluid. The new passive hydraulic engine mount design concept and its mathematical model are presented in details and some discussions on the simulation results are also included.