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Abstract
The purpose of this Milwaukee School of Engineering (MSOE) Master of Science in Engineering (MSE) Capstone Project Report is to present the results of a project featuring a multi-degree-of-freedom planar model of a motorcycle with an isolated powertrain to investigate the sensitivity of ride comfort to the rear powertrain mounting system with a specific focus on the mounting system’s stiffness, position, and damping. All models were developed in MATLAB to solve for natural frequencies, mode shapes, displacement transmissibility, and power spectral density (PSD) acceleration. The changes to PSD acceleration for the aspects of the model most relevant to ride comfort, i.e. sprung mass bounce and sprung mass pitch, were investigated. Results indicate that the behavior of the PSD acceleration results for sprung mass bounce and sprung mass pitch fall within expectations based on prior literature. Additionally, investigations into stiffness variation show a notable decrease in maximum PSD acceleration for sprung mass bounce with inconclusive results for sprung mass pitch. Moving the rear isolator down and away from the powertrain center of gravity (COG) results in a comparatively smaller decrease in maximum sprung mass bounce PSD acceleration, but sprung mass pitch shows a uniform decrease. Damping increases show the greatest amount of maximum PSD acceleration decrease for both sprung mass pitch and sprung mass bounce. Finally, four combinations of damping and stiffness parameters feature conflicting results for the significance of stiffness and damping contributions to reducing PSD acceleration for the sprung mass. The investigation into the above areas needs to be expanded in the future to validate results with experimental data and by investigating the full behavior changes to PSD acceleration plots, as opposed to solely inspecting PSD acceleration maxima; this will capture changes to other peaks and bandwidths that may impact qualitative and quantitative assessment of ride comfort. Additionally, the model can be augmented with a representation of specific rider interfaces such as hands, feet, and torso, along with investigations into different parameters, such as varying vehicle speed and different road input types. Such an analytical model in conjunction with experimental validation will provide a more complete understanding of the ride comfort sensitivity to the rear powertrain mounting system.