Role of spectrally varying mount properties in influencing coupling between powertrain motions under torque excitation

The influence of spectrally varying mount properties (including stiffness and damping) on the dynamics of powertrain motions is analytically examined. To overcome the deficiency of the direct inversion method (limited to only the frequency domain analysis), two methods are developed that describe the mount elements via a transfer function (in Laplace domain) or analogous mechanical model. New analytical formulations are verified by comparing the frequency responses with numerical results obtained by the direct inversion method (based on Voigt type mount model). Eigensolutions and transient responses of a spectrally varying mounting system are also predicted from new models. Based on complex eigenstructure, new coupling indices, including modal kinetic energy fractions, are defined for each method. Complex eigenvalue problem formulation with spectrally varying properties provides a closer match with measured natural frequencies than the real eigensolution with frequency-independent mounts. Given spectral variance in the mount properties, a simple roll mode decoupling scheme is suggested for the powertrain isolation system. Finally, an axiom for torque roll axis decoupling is provided by employing direct and adjoint eigenvalue problems.