Most of the prior work on active mounting systems has been conducted in the context of a single degree-offreedom even though the vehicle powertrain is a six degree-of-freedom isolation system.We seek to overcome this deficiency by proposing a new six degreeof-freedom analytical model of the powertrain system with a combination of active and passive mounts. All stiffness and damping elements contain spectrallyvarying properties and we examine powertrain motions when excited by an oscillating torque. Two methods are developed that describe the mount elements via a transfer function (in Laplace domain). 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 of a spectrally varying mounting system are also predicted by new models. Complex eigenvalue problem formulation with spectrally-varying properties provides a closer match with experimental results than the real eigenvalue formulation with frequencyindependent mounts. Given the spectral variance in the mount properties, a simple roll mode decoupling scheme is suggested for the powertrain isolation system. Then, the role of active path is clarified by comparison with no actuator operation.Multi-dimensional motions (especially coupling) are predicted and in particular the effects of active mount parameters such as the orientation angle, location and actuator input are investigated from the motion coupling perspective.
Several mounting system design concepts have been conceptually used to decouple the engine roll mode though limited success is observed in practice. One shortcoming of the existing theories is that they ignore damping in their formulations.To overcome this deficiency, we re-formulate the problem for a nonproportionally damped, linear system while recognizing that significant damping may be possible with passive (such as hydraulic), adaptive or active mounts. Only rigid body modes of power train are considered and chassis is assumed to be rigid. Complex mode method is employed and the torque roll axis (TRA) paradigms are re-examined in terms of mount rate ratios, mount locations and orientation angles. We will show that true TRA decoupling is not possible with non-proportional damping though it is theoretically achieved for a proportionally damped system. Results for both steady state (in the form of frequency response functions) and transient (given impulsive excitations) responses will be illustrated. The natural modes obtained using complex eigensolution method are coupled for the nonproportional damping case, even though they are completely decoupled for the proportional damping case. It is also seen that a higher value of non-proportionality induces more coupling between the rigid body motions of a powertrain. Our method and results are expected to lead to a better design of the mounting systems.
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