Of the various types of passive engine mounts, hydraulic engine mounts (HEMs) have the best noise, vibration and harshness (NVH) performance. Based on the third type HEM, which has an inertia track, decoupler and disturbing plate, the influences of the three hydraulic mechanisms, the length of the inertia track or the diameter of the orifice on the dynamic properties were studied experimentally. The working principles of the hydraulic mechanisms and the relationship between the dynamic properties of the three type HEMs were revealed clearly. It was discovered that the frequency-variant dynamic properties of HEMs with an inertia track or an orifice have excitation amplitude-invariant fixed points. Based on the theory of engineering hydromechanics, a nonlinear lumped parameter model (LPM) for an HEM with an inertia track was established, and an analytical solution was obtained in which the fixed point of dynamic stiffness in-phase was discovered theoretically. According to the phenomena of fixed points and the constant value of dynamic stiffness in-phase at higher bands, a new parameter identification method (PIM) was presented, which is clear in theory and is time and cost savings, the identified results are reliable. The results show that the fluid flow through an orifice can be replaced by a fluid flow through an equivalent length of inertia track. After this, a PIM for the fluid-flow local loss factor was developed. The identified results and the numerical simulations show that the reason the disturbing plate can keep the dynamic stiffness lower at higher bands is that the disturbing plate can sharply increase the quadratic fluid damping due to larger local loss, and then the resonance of the fluid flow through the decoupler channel or orifice is greatly attenuated. This conclusion is a useful attempt to explain the working principle of the disturbing plate. (c) 2007 Elsevier Ltd. All rights reserved.
