Effective reduction of stiffness at peak frequency in hydraulic engine mounts by using magneto-rheological fluids

Hydraulic engine mounts are generally used in aerospace and automotive applications for the purpose of cabin noise and vibration reduction. By careful selection of hydraulic mount design parameters, at a certain frequency, namely the notch frequency, the dynamic stiffness will be smaller than the static stiffness and cabin vibration and noise reduction is provided at that frequency. Literature review indicates that in all previous designs of hydraulic engine mounts the dynamic stiffness increases after the notch frequency. This phenomenon undesirable because of the increase in the force transmitted to the cabin. This paper proposes a new hydraulic engine mount that uses two working fluids. The new design has two notch frequencies and two peak frequencies. In this study, effective reduction of the peak frequencies has been demonstrated by using a controllable fluid as one of the working fluids and a non-controllable fluid as the second working fluid. As a result, one can obtain a hydraulic engine mount design with only one notch frequency but having no peak frequency. The new hydraulic engine mount design and its mathematical model are presented in detail and some discussions on the simulation results are provided.