| This dissertation analytically examines the multi-dimensional mounting schemes of an automotive engine-gearbox system when excited by oscillating torques or forces. The issue of torque roll axis decoupling is investigated first in significant detail since it is poorly understood. New dynamic decoupling axioms are presented and compared with the conventional elastic axis mounting and focalization methods. Several simplified physical systems are considered and new closed form solutions for symmetric and asymmetric engine mounting systems are developed. Our method is validated by comparing modal solutions with prior experimental and analytical studies. Parametric design studies are carried out to illustrate the methodology. Next a torsion box is constructed and instrumented for the study of torque roll axis decoupling concepts. A new measurement procedure for simultaneously estimating both normal and shear stiffness rates of rubber mounts is also proposed. The experimental study of the torsion box validates the theoretical concepts, however the flexible foundation effects must be incorporated in the analytical model.; Complications arising due to the spectrally varying and/or amplitude-dependent mount parameters are categorized next, and the associated eigenvalue and frequency response problems are defined. The real and complex eigenvalue problems that include both viscous and visco-elastic damping models are critically examined and illustrated via examples. A nonlinear eigenvalue problem is formulated and the resulting eigensolutions are determined for a discrete system with frequency-dependent elastic and dissipative parameters. Several approximate methods, including the modal expansion method, are also proposed to calculate the forced harmonic response, and their solution errors are assessed. A quasi-linear method is applied to a 1/2 car model, using measured data of a typical hydraulic engine mount, to see the effect of excitation amplitude-dependent dynamic stiffnesses. A refined nonlinear, frequency domain synthesis method is also proposed that includes local nonlinearities in the form of measured dynamic stiffness data. The forced harmonic response of the overall system is obtained, and the proposed method is validated by comparing it with the corresponding time domain method for a specific 1/4 car model. |
