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There is the possibility of decoupler’s impact noise in hydraulic engine mount (HEM) with a free decoupler, but there is little research on this aspect. As for how to solve the problem of decoupler’s impact noise, most of the papers are only improved through trial and error. This article uses three HEMs with different decoupler plates and cages as the research object for the experiment. First, calculate the contact force between the decoupler plate and cage of the HEM through the finite element method, to determine whether the decoupler’s impact noise problem will occur. Then design the bench test of the abnormal noise of the HEMs to verify the conclusion obtained by the calculation of the contact force. Next, deduce the relationship between the transmitted force at the chassis side of the HEM and the impact force of the decoupler, and propose a test method for evaluating the decoupler’s impact noise based on the transmitted force at the chassis side of the HEM.

The amplitude-sensitive nonlinear mathematical model of the hydraulic engine mount (HEM) with a free-floating decoupler is deduced through the theory of fluid dynamics. The model considers the amplitude-sensitive characteristics, such as local pressure loss of the inertial track and the decoupler, the amplitude-sensitive dynamic stiffness of main rubber, and the switch mechanism of the decoupler. A new model of decoupler’s switching mechanism is established, which makes parameter identification simpler comparing to the existing analogous models. The finite element method is used to identify parameters of the lumped-parameter model, such as the contact force between the decoupler plate and the cage, the stiffness of the main rubber, the equivalent piston area, the chambers’ compliances, etc. The lumped parameters of fluid track are obtained by fluid mechanics formula.