Nonlinear frequency responses of quarter vehicle models with amplitude-sensitive engine mounts

Although the amplitude dependence of engine mounts has been widely studied via experimental and analytical studies, its effect on the vehicle system response is still unclear. Therefore, the chief goal of this paper is to develop a method that will incorporate measured dynamic stiffness properties of the isolator and predict the resulting amplitude-dependent nonlinear behavior of the governing system in the frequency domain. Experimental data on two hydraulic engine mount concepts, namely the inertia track and free decoupler mounts, are incorporated to illustrate realistic amplitude dependence. Then, nonlinear frequency responses of two quarter vehicle models, up to 50 Hz, are analytically calculated using the one-term harmonic balance method. Our analysis shows that the proposed semi-analytical scheme should be employed, instead of ad hoc methods, when the mount parameters are amplitude-sensitive. In particular, the inclusion of inertia track mount leads to the softening effect. A comparison with Duffing's oscillator is made to qualitatively assess its nature. A system with the free decoupler mount looks more like a linear time-invariant system, at least from the frequency response perspective, due to high decoupler damping that negates the amplitude sensitivity. Finally, some numerical convergence issues are briefly discussed.