Optimum Design of Passive Vibration Isolator for a Box in a Vehicle Based on the Random Vibration Theory

In this paper the behavior of a sensitive box to vibration¡ which connected to the vehicle by means of four undamped passive vibration isolator mounts¡ is studied using a ten DOF model to the road excitation. First¡ the governing differential equations are obtained using the Lagrange method¡ and the power spectral density (PSD) of the road profile is determined based on the ISO. The natural frequencies and mode shapes are extracted using modal analysis¡ and the response to the random base excitation is calculated based on random vibration theory. The root of mean square (RMS) is calculated by integration of PSD curve. The RMS of vertical acceleration of the box is plotted vs. the RMS of its relative vertical displacement by varying the stiffness of isolators in a real interval and the optimal stiffness is selected as the minimum point on the curve. The results indicate that the optimum isolator can be selected gardless of wheels and suspension system and the natural frequencies of isolator are between the natural frequencies of wheels and of suspension system. The RMS of acceleration the box has low sensitivity to the variation of the isolator stiffness around the optimum point.