Influence of a Vibration Isolation System on Planar Dynamics of a Motorcycle

This paper examines a model to investigate the impact of a vibration isolation system on the planar (in-plane) dynamics of a motorcycle. While it is not very common, a vibration isolation system is used in some motorcycles to mitigate vibrations resulting from the shaking forces of the engine. For such layouts, the powertrain is assembled to the frame through the vibration isolation system that typically consists of two to four isolators. It is critical to comprehend the influence of the isolation system on the overall dynamic characteristics of the motorcycle due to the coupled dynamics of the rear suspension, the isolation system, and the rear unsprung mass. The influence of a vibration isolation system on the in-plane dynamics is analysed by using a relatively simple model that has been developed in this study. This model has been used to evaluate the influence of the isolation system on natural modes, transmissibility, and ride comfort. Results indicate that the use of a vibration isolation system couples the rear unsprung hop to the pitch motion of the powertrain with a slight increase in the corresponding natural frequency. Results indicate that the use of a vibration isolation system directly affects handling of the motorcycle. Furthermore, results indicate that the pitch of the sprung mass and the hop of the rear unsprung mass are particularly influenced by the vibration isolation system. The model presented in this paper could be useful in the early stages of the design process to compare the rigidly mounted powertrain to different layouts of the vibration isolation system.